U.S. patent application number 15/171566 was filed with the patent office on 2016-12-15 for magnetic field measurement apparatus and magnetic field measurement method.
This patent application is currently assigned to SEIKO EPSON CORPORATION. The applicant listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Akihiro DEGUCHI, Ryuji HOKARI, Mitsutoshi MIYASAKA, Toshihiro SAITO.
Application Number | 20160360987 15/171566 |
Document ID | / |
Family ID | 57516436 |
Filed Date | 2016-12-15 |
United States Patent
Application |
20160360987 |
Kind Code |
A1 |
MIYASAKA; Mitsutoshi ; et
al. |
December 15, 2016 |
MAGNETIC FIELD MEASUREMENT APPARATUS AND MAGNETIC FIELD MEASUREMENT
METHOD
Abstract
A magnetic field measurement apparatus includes a magnetic
sensor that detects a magnetic field from a subject, a table on
which the subject is mounted, a shape measurement device that
measures a surface shape of the subject, an average plane
calculation unit that calculates an average plane of the surface
shape, and a control unit that controls the table so that an
opposing surface of the magnetic sensor is parallel to the average
plane.
Inventors: |
MIYASAKA; Mitsutoshi;
(Suwa-shi, JP) ; SAITO; Toshihiro; (Suwa-shi,
JP) ; DEGUCHI; Akihiro; (Chino-shi, JP) ;
HOKARI; Ryuji; (Chino-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
57516436 |
Appl. No.: |
15/171566 |
Filed: |
June 2, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B 5/0077 20130101;
G01R 33/025 20130101; A61B 5/04008 20130101; G01R 33/0076 20130101;
A61B 5/04007 20130101; A61B 5/1077 20130101; A61B 5/0046 20130101;
G01R 33/0358 20130101; A61B 5/1072 20130101; A61B 5/704 20130101;
A61B 5/0064 20130101 |
International
Class: |
A61B 5/04 20060101
A61B005/04; A61B 5/00 20060101 A61B005/00; G01R 33/035 20060101
G01R033/035 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 2015 |
JP |
2015-116409 |
Claims
1. A magnetic field measurement apparatus comprising: a detection
unit that detects a magnetic field from a subject and that
possesses a first surface; a table on which the subject is mounted;
a measurement unit that measures a surface shape of the subject; a
calculation unit that calculates an average plane of the surface
shape; and a control unit that controls the table so that the first
surface is parallel to the average plane.
2. The magnetic field measurement apparatus according to claim 1,
wherein the control unit controls the table so that the distance
between the first surface and the subject becomes a predetermined
distance.
3. The magnetic field measurement apparatus according to claim 1,
further comprising: a magnetic shield unit that encloses the
detection unit and the table, includes an opening through which the
subject comes in and out, and attenuates an external magnetic
field, wherein the measurement unit is provided in the opening.
4. The magnetic field measurement apparatus according to claim 1,
wherein the measurement unit scans the subject with a first
light.
5. The magnetic field measurement apparatus according to claim 4,
further comprising: a guide light irradiation unit that irradiates
a second light for guiding a position where the subject is mounted,
wherein the measurement unit is also used as the guide light
irradiation unit.
6. The magnetic field measurement apparatus according to claim 1,
wherein the table includes a plurality of leg portions, and the
control unit controls lengths of the leg portions so as to tilt the
subject.
7. The magnetic field measurement apparatus according to claim 3,
wherein a portion of the table is non-magnetic.
8. The magnetic field measurement apparatus according to claim 1,
wherein a location where the detection unit detects a magnetic
field is on the heart.
9. A magnetic field measurement method comprising: mounting a
subject on a table; measuring a surface shape of the subject;
calculating an average plane of the subject; tilting the table so
that a first surface of a detection unit is parallel to the average
plane; causing the subject to come close to the first surface; and
causing the detection unit to detect a magnetic field from the
subject.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a magnetic field
measurement apparatus and a magnetic field measurement method.
[0003] 2. Related Art
[0004] A magnetic field measurement apparatus for measuring a
magnetic field of the heart or a magnetic field of the brain,
weaker than terrestrial magnetism, has been studied. The magnetic
field measurement apparatus is noninvasive, and can measure states
of organs without applying a load to a subject. JP-A-2001-170018
discloses a magnetic field measurement apparatus which measures a
magnetic field of the heart by using a magnetic detection sensor.
According to JP-A-2001-170018, the apparatus includes a table, and
a person as a subject is mounted on the table. A superconducting
quantum interference element is used in the magnetic detection
sensor.
[0005] The table can be moved in three directions which are
orthogonal to each other. The subject is positioned by using laser
light. It is assumed that the three directions which are orthogonal
to each other are XYZ directions, and a surface on which the
subject is mounted corresponds to an XY plane. First, first laser
light is applied obliquely in an XZ plane toward the table, and
second laser light is applied obliquely in a YZ plane. In addition,
third laser light advancing in the Z direction is applied. The
first laser light, the second laser light, and the third laser
light intersect each other at a reference point. The reference
point is a position which does not move relative to the table.
[0006] When the table is moved to a location opposing the magnetic
detection sensor, the distance between the magnetic detection
sensor and the reference point is a known distance. A subject is
mounted on the table. At this time, the reference point is used as
a mark, and a position of the subject is measured. The table is
moved so that the chest on the heart side of the subject is located
at an appropriate location within a measurement range of the
magnetic detection sensor. A height of the table is adjusted so
that the distance between the magnetic detection sensor and the
chest of the subject is an appropriate distance. In this case, a
position of the subject can match the magnetic detection sensor
with high accuracy by using a measurement value of the distance
between the reference point which is clearly shown by the laser
light and the chest of the subject.
[0007] In the magnetic field measurement apparatus disclosed in
JP-A-2001-170018, the table is moved so that a relative position
between the superconducting quantum interference element and the
subject becomes an appropriate position, but there is a problem in
that detection accuracy is low. Therefore, a magnetic field
measurement apparatus which can detect a distribution of magnetic
vectors of a subject is desirable.
SUMMARY
[0008] An advantage of some aspects of the invention is to solve
the problems described above, and the invention can be implemented
as the following aspects or application examples.
Application Example 1
[0009] A magnetic field measurement apparatus according to this
application example includes a detection unit that detects a
magnetic field from a subject; a movable table on which the subject
is mounted; a measurement unit that measures a surface shape of the
subject; a calculation unit that calculates an average plane of the
surface shape; and a control unit that controls the movable table
so that an opposing surface to the subject in the detection unit is
parallel to the average plane.
[0010] According to the present inventor's intensive examination,
in the magnetic field measurement apparatus of the related art as
disclosed in JP-A-2001-170018, when a subject is mounted on the
table, a normal direction of an average plane of the subject
differs depending on a body shape of the subject. When a normal
direction of an average plane of the chest of the subject is
inclined with respect to a direction in which the magnetic
detection sensor detects a magnetic vector, an average plane of a
surface of the chest and a surface of the magnetic detection sensor
on the chest side are not parallel to each other, but intersect. In
this case, there may be the occurrence of a location where the
distance between the surface of the chest and the magnetic
detection unit is short and a location where the distance
therebetween is long. A weaker magnetic vector is detected at a
location where the distance between the surface of the chest and
the magnetic detection sensor is short than a vector at a location
where the distance therebetween is long. For this reason, it has
been proven in the magnetic field measurement apparatus of the
related art that detection accuracy is reduced. In contrast,
according to this application example, the magnetic field
measurement apparatus includes the movable table, and a subject is
mounted on the movable table. The measurement unit measures a
surface shape of a measured portion of the subject. Next, the
calculation unit calculates an average plane of the surface shape
of the subject. The surface shape of the subject is a curved
surface, and the calculation unit defines the average plane so that
deviation of the measurement unit relative to the surface shape is
the minimum. Next, the control unit controls a tilt of the movable
table so that the opposing surface is parallel to the average
plane. In a state in which the opposing surface of the detection
unit is parallel to the average plane, an average distance between
the average plane and the opposing surface is shortened, and the
detection unit detects a magnetic field coming out of the subject.
As a result, the magnetic field measurement apparatus of the
application example can detect a distribution of magnetic vectors
of the subject with high accuracy without being influenced by a
subject's body shape.
[0011] As the subject and the opposing surface become more distant
from each other, a magnetic field reaching the opposing surface
becomes weaker, and thus a signal-to-noise ratio (S/N ratio) of a
signal output from the detection unit is lowered. In contrast, if
the subject is in contact with the opposing surface, the detection
unit receives vibration from the subject, and noise increases due
to the vibration. In the application example, the control unit can
control a tilt of the movable table so as to make the average plane
parallel to the opposing surface of the detection unit, and can
cause the subject to sufficiently come close to the opposing
surface in a range in which there is no contact therebetween. As a
result, the detection unit can detect a magnetic field coming out
of the subject with high sensitivity.
Application Example 2
[0012] In the magnetic field measurement apparatus according to the
application example, the control unit may control the movable table
so that the distance between the opposing surface and the subject
becomes a predetermined distance.
[0013] According to this application example, the control unit
controls the movable table so that the distance between the
opposing surface and the subject becomes a predetermined distance.
The predetermined distance is longer than the distance which the
surface shape of the subject varies through a normal action of the
subject such as breathing. The predetermined distance is short
within a range in which the subject is not in contact with the
detection unit. The control unit controls the movable table so that
the distance between the subject and the opposing surface becomes a
distance which does not cause contact therebetween due to a normal
action of the subject. As a result, the subject can be made to come
close to the detection unit within a range in which the subject is
not in contact therewith.
Application Example 3
[0014] The magnetic field measurement apparatus according to the
application example may further include a magnetic shield unit that
encloses the detection unit and the movable table, includes an
opening through which the subject comes in and out, and attenuates
an entering magnetic field line, and the measurement unit is
provided in the opening.
[0015] According to this application example, the magnetic field
measurement apparatus includes the magnetic shield unit. The
magnetic shield unit attenuates an external magnetic field (an
entering magnetic field line). The detection unit is provided
inside the magnetic shield unit so as to measure a magnetic field.
The magnetic shield unit includes the opening, and attenuates an
entering magnetic field line. Consequently, the detection unit can
perform measurement with less noise. The measurement unit is
provided in the opening through which the subject comes in and out.
Since the subject passes near the measurement unit, the measurement
unit can easily measure a surface shape of the subject.
Application Example 4
[0016] In the magnetic field measurement apparatus according to the
application example, the measurement unit may scan the subject with
a light beam, first light, and measure a location irradiated with
the light beam.
[0017] According to this application example, the measurement unit
scans the subject with a light beam. A location irradiated with the
light beam is measured. A surface shape of the subject has
unevenness, and the laser beam is reflected on the unevenness.
Therefore, the measurement unit can easily detect the surface shape
of the subject by detecting a position of the light beam reflected
from the subject.
Application Example 5
[0018] The magnetic field measurement apparatus according to the
application example may further include a guide light irradiation
unit that applies a light beam for guiding a position where the
subject is mounted, and the measurement unit may also be used as
the guide light irradiation unit, and the measurement unit may
apply a light beam for guiding a position where the subject is
mounted. The guide light irradiation unit irradiates a second light
for pointing where the subject is mounted.
[0019] According to this application example, the measurement unit
has a function of a guide light irradiation unit which applies a
light beam for guiding a position where the subject is mounted on
the movable table, and a function of measuring a surface shape of
the subject. The subject is positioned targeting a location
indicated by the light beam, and thus the subject can be mounted at
a predetermined position on the movable table. The measurement unit
also has a function of measuring a surface shape of the subject by
scanning the subject with a light beam. Therefore, it is possible
to reduce the number of constituent elements of the magnetic field
measurement apparatus compared with a case where the magnetic field
measurement apparatus separately includes the guide light
irradiation unit and the measurement unit. As a result, it is
possible to manufacture the magnetic field measurement apparatus
with high productivity.
Application Example 6
[0020] In the magnetic field measurement apparatus according to the
application example, the movable table may include a plurality of
leg portions, and the control unit may control lengths of the leg
portions so as to tilt the subject.
[0021] According to this application example, the movable table
includes a plurality of leg portions. The control unit controls
lengths of the leg portions so as to tilt the subject on the
movable table. Consequently, the average plane of the subject can
be made parallel to the opposing surface. The movable table may
have a structure in which a device controlling a tilt is provided
at the center thereof. In contrast to this structure, in the
application example, loads of the movable table and the subject can
be distributed to the plurality of leg portions. Therefore, it is
possible to control a tilt of the movable table by using the leg
portions with a lightweight structure.
Application Example 7
[0022] In the magnetic field measurement apparatus according to the
application example, a portion of the movable table which is moved
into the magnetic shield unit may be non-magnetic.
[0023] According to this application example, a portion of the
movable table which can be moved into the magnetic shield unit is
non-magnetic. The non-magnetic portion does not influence
measurement of a magnetic field in the detection unit. Therefore,
it is possible to prevent magnetization of the movable table from
influencing measurement of a magnetic field.
Application Example 8
[0024] In the magnetic field measurement apparatus according to the
application example, a location where the detection unit detects a
magnetic field may be a surface of the chest opposing the
heart.
[0025] According to this application example, a location where the
detection unit detects a magnetic field is a surface of the chest
opposing the heart. A magnetic field generated due to the activity
of the heart is output from the surface of the chest. As a result,
the detection unit can detect the activity of the heart.
Application Example 9
[0026] A magnetic field measurement method according to this
application example includes mounting a subject on a movable table;
measuring a surface shape of the subject; calculating an average
plane of the subject; tilting the movable table so that an opposing
surface to the subject in a detection unit is parallel to the
average plane; causing the subject to come close to the opposing
surface; and causing the detection unit to detect a magnetic field
from the subject.
[0027] According to this application example, the subject is
mounted on the movable table, and a surface shape of the subject is
measured. An average plane of the subject is calculated. The
subject is curved, and the average plane is defined so that
deviation with the surface shape of the subject is the minimum.
Next, a tilt of the movable table is controlled so that an opposing
surface of a detection unit is parallel to the average plane of the
subject. The subject is made to come close to the opposing surface
of the detection unit, and the detection unit detects a magnetic
field coming out of the subject.
[0028] In this application example, the average plane of the
subject is calculated. The control unit controls a tilt of the
movable table so that the average plane is parallel to the opposing
surface of the detection unit. The subject comes close to the
opposing surface without making contact therebetween. Therefore,
the subject is made to come close to the opposing surface in a form
in which the subject hardly contacts the detection unit. As a
result, the detection unit can detect a magnetic field coming out
of the subject with high sensitivity.
Application Example 10
[0029] A living body magnetic field measurement apparatus according
to this application example includes a magnetic detection unit that
detects a distribution of a component in a first direction of a
magnetic vector on a first surface of a subject; a table on which
the subject is mounted in a state of being in contact with a second
surface opposite to the first surface, and that includes a contact
surface in contact with the second surface; a measurement unit that
measures shapes of the first surface and the second surface; and a
control unit that sets a normal direction of the first surface to
be the same as the first direction, and controls a shape of the
contact surface to be a shape corresponding to the shape of the
second surface.
[0030] According to this application example, the living body
magnetic field measurement apparatus includes the magnetic
detection unit, and the magnetic detection unit detects a
distribution of a component in a first direction of a magnetic
vector on a first surface of a subject. The subject is mounted on a
table. The first surface of the subject is directed toward the
magnetic detection unit, and the second surface thereof is directed
toward the table, and thus the second surface is in contact with
the contact surface of the table. The measurement unit measures
shapes of the first surface and the second surface. The control
unit controls a shape of the contact surface to be a shape
corresponding to the shape of the second surface, and sets a normal
direction of the first surface of the subject to be the same as the
first direction.
[0031] Therefore, the normal direction of the first surface of the
subject can be adjusted to a direction in which the sensitivity of
the magnetic detection unit is high. If the normal direction of the
first surface is inclined with respect to the first direction,
there may be the occurrence of a location where the distance
between the first surface and the magnetic detection unit is short
and a location where the distance therebetween is long. The weaker
strength of a magnetic vector is detected at the location where the
distance between the first surface and the magnetic detection unit
is short than a vector at the location where the distance
therebetween is long, and thus detection accuracy is reduced. In
the application example, the normal direction of the first surface
is the same as the first direction. As a result, it is possible to
detect the distribution of the magnetic vector of the subject with
high accuracy.
Application Example 11
[0032] In the living body magnetic field measurement apparatus
according to the application example, the contact surface may be
divided into a plurality of division surfaces moved in the first
direction, and the number of division surfaces may be 10 or larger
and 20 or smaller.
[0033] According to this application example, the contact surface
is divided into a plurality of division surfaces moved in the first
direction. Positions of the plurality of division surfaces in the
first direction match the subject, and thus the contact surface can
be made to correspond to a shape of the second surface. The number
of the plurality of division surfaces is equal to or larger than
10. Therefore, since the ten or more division surfaces are in
contact with and support the subject, the subject can be stably
supported, and the first surface can be made to be directed in a
predetermined direction. The number of the plurality of division
surfaces is equal to or smaller than 20. Therefore, the control
unit can easily control positions of the division surfaces.
Application Example 12
[0034] In the living body magnetic field measurement apparatus
according to the application example, a width of each of the
division surfaces may be equal to or more than 5 cm and equal to or
less than 15 cm.
[0035] According to this application example, a width of each of
the division surfaces is equal to or more than 5 cm and equal to or
less than 15 cm. Therefore, since the division surfaces are in
contact with and support the subject at the interval of 5 cm to 15
cm, the subject can be stably supported, and the first surface can
be directed in a predetermined direction.
Application Example 13
[0036] In the living body magnetic field measurement apparatus
according to the application example, a movable range in which the
division surfaces are moved in the first direction may be equal to
or more than 3 cm and equal to or less than 10 cm.
[0037] According to this application example, a movable range of
the division surfaces is equal to or more than 3 cm and equal to or
less than 10 cm. In this case, if the subject is a person, the
contact surface can match a shape of the back side of the person.
Thus, since the division surfaces are in contact with and support
the subject, the subject can be stably supported, and the first
surface can be directed in a predetermined direction. Since the
movable range is equal to or less than 10 cm, it is possible to
easily control the division surfaces.
Application Example 14
[0038] The living body magnetic field measurement apparatus
according to the application example may further include a magnetic
shield unit that encloses the magnetic detection unit and the
table, includes a first opening through which the subject comes in
and out, and attenuates an entering magnetic field line, and the
control unit is present at a location separated from the first
opening.
[0039] According to this application example, the living body
magnetic field measurement apparatus includes the magnetic shield
unit. The magnetic shield unit attenuates an entering magnetic
field line. The magnetic detection unit and the table are provided
inside the magnetic shield unit, and a magnetic field is measured.
The magnetic shield unit is provided with the first opening, and
the subject can come in and out through the first opening.
[0040] The control unit controlling the table is present at a
location separated from the first opening. The control unit makes
an electric signal flow so as to control the table. A magnetic
field or a residual magnetic field is generated due to the electric
signal, and becomes noise when detected by the magnetic detection
unit. In the application example, since the control unit is present
at the location separated from the first opening, the magnetic
field or the residual magnetic field generated from the control
unit hardly reaches the magnetic detection unit. As a result, the
magnetic detection unit can perform measurement with less
noise.
Application Example 15
[0041] In the living body magnetic field measurement apparatus
according to the application example, the magnetic shield unit may
include a tube through which the inside and the outside of the
magnetic shield unit communicate with each other, and the tube
extends in a direction orthogonal to the first direction.
[0042] According to this application example, the magnetic shield
unit includes the tube through which the inside and the outside of
the magnetic shield unit communicate with each other, and the tube
extends in a direction orthogonal to the first direction. A
direction of a magnetic vector passing through the tube is
orthogonal to the first direction. Therefore, a magnetic vector
passing through the tube hardly influences the magnetic detection
unit. As a result, the magnetic detection unit can perform
measurement with less noise.
Application Example 16
[0043] In the living body magnetic field measurement apparatus
according to the application example, the magnetic shield unit may
have a tubular shape extending in a second direction orthogonal to
the first direction, and the tube extends in the second direction
along the magnetic shield unit.
[0044] According to this application example, the tube extends in
the second direction, and the second direction is orthogonal to the
first direction. Therefore, a magnetic vector passing through the
tube hardly influences the magnetic detection unit. As a result,
the magnetic detection unit can perform measurement with less
noise. Since the tube is provided along the magnetic shield unit,
the tube is easily fixed to the magnetic shield unit. Thus, it is
possible to easily provide the tube.
Application Example 17
[0045] A living body magnetic field measurement method according to
this application example includes measuring shapes of a first
surface of a subject and a second surface opposing the first
surface; calculating a shape of the second surface when a normal
direction of the first surface is set to be the same as a direction
of a component in a first direction in which a magnetic detection
unit detects a magnetic vector distribution; forming a contact
surface of a table which is in contact with the subject in a shape
corresponding to the shape of the second surface; mounting the
subject on the contact surface of the table; and causing the first
surface to come close to the magnetic detection unit so that the
distribution of the component in the first direction of the
magnetic vector in the subject is detected.
[0046] According to this application example, shapes of the first
surface and the second surface of the subject are measured. The
second surface opposes the first surface. The first surface is a
surface for detecting the strength of a magnetic vector in the
magnetic detection unit, and the second surface is a surface on
which the subject is in contact with the contact surface of the
table. The magnetic detection unit detects the component in the
first direction of the magnetic vector on the first surface. Next,
a shape of the second surface when a normal direction of the first
surface is set to be the same as the component in the first
direction is calculated. In the calculation, a position and a tilt
of the shape of the second surface obtained when the subject is
mounted on the table are calculated.
[0047] Next, the contact surface of the table is formed in a shape
corresponding to the shape with the calculated tilt. Successively,
the subject is mounted on the contact surface of the table. The
contact surface has the shape corresponding to the shape of the
second surface of the subject, and the subject is mounted so that
the second surface thereof is in contact with the contact surface.
At this time, the first surface of the subject is directed in the
first direction. Next, the first surface is caused to come close to
the magnetic detection unit. It is possible to increase the
sensitivity of the magnetic detection unit through the approach.
The distribution of the component in the first direction of the
magnetic vector in the subject is detected.
[0048] Through the above-described procedures, the first direction
can match the normal direction of the first surface of the subject.
If the normal direction of the first surface is inclined with
respect to the first direction, there may be the occurrence of a
location where the distance between the first surface and the
magnetic detection unit is short and a location where the distance
therebetween is long. The weaker strength of a magnetic vector is
detected at the location where the distance between the first
surface and the magnetic detection unit is short than a vector at
the location where the distance therebetween is long, and thus
detection accuracy is reduced. In the application example, the
detection strength of a magnetic vector in the first surface can be
made uniform. As a result, it is possible to detect the
distribution of the magnetic vector of the subject with high
accuracy.
Application Example 18
[0049] A living body magnetic field measurement apparatus according
to this application example includes a magnetic detection unit that
detects a magnetic field coming out of a measured surface of a
subject; a position measurement unit that measures a position of
the measured surface in a first direction relative to the magnetic
detection unit; a table on which the subject is mounted and that
moves the subject; and a control unit that controls the table so
that a distance in the first direction between the measured surface
and the magnetic detection unit becomes a predetermined
distance.
[0050] According to this application example, the living body
magnetic field measurement apparatus includes the magnetic
detection unit, the position measurement unit, the table, and the
control unit. The magnetic detection unit detects a magnetic vector
coming out of a measured surface of a subject. The position
measurement unit measures a position of the measured surface in the
first direction. The subject is mounted on the table, and the table
moves the subject. The control unit controls a position of the
table. The control unit controls a distance by which the table is
moved on the basis of data regarding a position of the measured
surface relative to the magnetic detection unit, measured by the
position measurement unit. The control unit performs control so
that the distance in the first direction between the measured
surface and the magnetic detection unit becomes a predetermined
distance. If the magnetic detection unit becomes distant from the
measured surface, the strength of a magnetic field detected by the
magnetic detection unit is in inverse proportion to the square of a
distance from the measured surface. Therefore, detection
performance of the magnetic detection unit is reduced as the
magnetic detection unit becomes more distant from the measured
surface. Since the magnetic detection unit vibrates when the
measured surface is in contact with the magnetic detection unit,
the measurement accuracy is reduced. In the application example,
the measured surface can be made to come close to the magnetic
detection unit in a range in which the measured surface is not in
contact with the magnetic detection unit. The position measurement
unit measures a position of the measured surface relative to the
magnetic detection unit, and then the table causes the subject to
come close to the magnetic detection unit. Therefore, even if the
position measurement unit is separated from the magnetic detection
unit, the subject can be made to come close to the magnetic
detection unit. As a result, the living body magnetic field
measurement apparatus can detect a magnetic field of the measured
surface with high accuracy.
Application Example 19
[0051] In the living body magnetic field measurement apparatus
according to the application example, the table may move the
subject in a second direction and a third direction, the second
direction and the third direction may be orthogonal to the first
direction, and the second direction and the third direction may
intersect each other.
[0052] According to this application example, the table moves the
subject in the second direction and the third direction. The second
direction and the third direction are orthogonal to the first
direction. The second direction and the third direction intersect
each other. Therefore, the table can move the subject in a
direction along a plane orthogonal to the first direction. As a
result, the table can easily position the subject in the plane
direction orthogonal to the first direction.
Application Example 20
[0053] In the living body magnetic field measurement apparatus
according to the application example, the second direction may be
orthogonal to the third direction.
[0054] According to this application example, the second direction
is orthogonal to the third direction. The table moves the subject
in the second direction and the third direction orthogonal to each
other. Therefore, the table can be moved according to the
orthogonal coordinate system, and thus it is possible to easily
control a movement position of the table.
Application Example 21
[0055] The living body magnetic field measurement apparatus
according to the application example may further include a magnetic
shield unit that encloses the magnetic detection unit, includes a
first opening through which the table comes in and out in the
second direction, and attenuates an entering magnetic field
line.
[0056] According to this application example, the living body
magnetic field measurement apparatus includes the magnetic shield
unit. The magnetic shield unit attenuates an entering magnetic
field line. The magnetic detection unit is provided inside the
magnetic shield unit so as to measure a magnetic field. The
magnetic shield unit includes a first opening and attenuates an
entering magnetic field line. Consequently, the magnetic detection
unit can perform measurement with less noise.
Application Example 22
[0057] In the living body magnetic field measurement apparatus
according to the application example, the position measurement unit
may measure a single location on the measured surface whose height
from the table is large.
[0058] According to this application example, the position
measurement unit measures a single location on the measured surface
of which a height from the table is large. Therefore, it is
possible to detect a position of a most protruding portion of the
measured surface. As a result, the measured surface can be made to
come close to the magnetic detection unit in a range in which the
most protruding portion does not come into contact with the
magnetic detection unit.
Application Example 23
[0059] In the living body magnetic field measurement apparatus
according to the application example, the position measurement unit
may measure a stereoscopic shape of the measured surface.
[0060] According to this application example, the position
measurement unit measures a stereoscopic shape of the measured
surface. Therefore, it is possible to detect a position of a most
protruding portion of the measured surface. As a result, the
measured surface can be made to come close to the magnetic
detection unit in a range in which the most protruding portion does
not come into contact with the magnetic detection unit.
Application Example 24
[0061] In the living body magnetic field measurement apparatus
according to the application example, the position measurement unit
may scan the measured surface with a light beam, and measures a
location irradiated with the light beam.
[0062] According to this application example, the position
measurement unit scans the measured surface with a light beam. A
location irradiated with the light beam is measured. Therefore, the
position measurement unit can detect a position of a most
protruding portion within a range in which scanning is performed
with the light beam.
Application Example 25
[0063] The living body magnetic field measurement apparatus
according to the application example may further include a guide
light irradiation unit that applies a light beam for guiding a
position where the subject is mounted, the position measurement
unit irradiates the subject with a light beam and performs
measurement, the position measurement unit is also used as the
guide light irradiation unit, and the position measurement unit
applies a light beam for guiding a position where the subject is
mounted.
[0064] According to this application example, the living body
magnetic field measurement apparatus has a function of a guide
light irradiation unit and a function of a position measurement
unit. The function of the guide light irradiation unit is a
function of applying a light beam for guiding a position where the
subject is mounted. The function of the position measurement unit
is a function of irradiating the subject with a light beam so as to
measure a shape of the subject. The position measurement unit is
also used as the guide light irradiation unit, and the position
measurement unit applies a light beam for guiding a position where
the subject is mounted. Therefore, it is possible to reduce the
number of constituent elements compared with a case where the
living body magnetic field measurement apparatus separately
includes the guide light irradiation unit and the position
measurement unit. As a result, it is possible to manufacture the
living body magnetic field measurement apparatus with high
productivity.
Application Example 26
[0065] In the living body magnetic field measurement apparatus
according to the application example, the position measurement unit
may be provided in the first opening.
[0066] According to this application example, the position
measurement unit is provided in the first opening. The subject
mounted on the table passes through the first opening. Therefore,
the subject passes near the position measurement unit, and thus the
position measurement unit can easily irradiate the subject with
light.
Application Example 27
[0067] In the living body magnetic field measurement apparatus
according to the application example, a portion of the table which
may be moved into the magnetic shield unit is non-magnetic.
[0068] According to this application example, a portion of the
table which can be moved into the magnetic shield unit is
non-magnetic. Therefore, it is possible to prevent magnetization of
the table from influencing measurement of a magnetic field.
Application Example 28
[0069] In the living body magnetic field measurement apparatus
according to the application example, the control unit may be
present at a location separated from the first opening.
[0070] According to this application example, the living body
magnetic field measurement apparatus includes the magnetic shield
unit. The magnetic shield unit attenuates an entering magnetic
field line. The magnetic detection unit and the table are provided
inside the magnetic shield unit, and a magnetic field is measured.
The magnetic shield unit is provided with the first opening, and
the subject can come in and out through the first opening.
[0071] The control unit controlling the table is present at a
location separated from the first opening. The control unit makes
an electric signal flow so as to control the table. A magnetic
field or a residual magnetic field is generated due to the electric
signal, and becomes noise when detected by the magnetic detection
unit. In the application example, since the control unit is present
at the location separated from the first opening, the magnetic
field or the residual magnetic field generated from the control
unit hardly reaches the magnetic detection unit. As a result, the
magnetic detection unit can perform measurement with less
noise.
Application Example 29
[0072] In the living body magnetic field measurement apparatus
according to the application example, the magnetic shield unit may
include a tube through which the inside and the outside of the
magnetic shield unit communicate with each other, and the tube may
extend in a direction orthogonal to the first direction.
[0073] According to this application example, the magnetic shield
unit includes the tube through which the inside and the outside of
the magnetic shield unit communicate with each other, and the tube
extends in a direction orthogonal to the first direction. A
direction of a magnetic vector passing through the tube is
orthogonal to the first direction. Therefore, a magnetic vector
passing through the tube hardly influences the magnetic detection
unit. As a result, the magnetic detection unit can perform
measurement with less noise.
Application Example 30
[0074] The living body magnetic field measurement apparatus
according to the application example may further include a driving
source that moves the table in the third direction, and the driving
source may include an attachment/detachment portion that is located
outside the magnetic shield unit and attaches or detaches the table
and the driving source to each other or from each other.
[0075] According to this application example, the driving source
moves the table in the third direction. The driving source includes
the attachment/detachment portion that is located outside the
magnetic shield unit and attaches or detaches the table and the
driving source to each other or from each other. Therefore, the
attachment/detachment portion connects the table to the driving
source, and thus the table can be moved in the third direction by
using the driving source. When the table is not moved in the third
direction, the attachment/detachment portion can detach the driving
source from the table. The driving source is located outside the
magnetic shield unit, and can move the table into the magnetic
shield unit. Therefore, it is possible for the inside of the
magnetic shield unit to be hardly influenced by a magnetic field of
the driving source. As a result, the magnetic detection unit can
perform measurement with less noise.
Application Example 31
[0076] The living body magnetic field measurement apparatus
according to the application example may further include a driving
source that moves the table in the second direction, and the
driving source is located outside the magnetic shield unit.
[0077] According to this application example, the driving source
moves the table in the second direction. The driving source is
located outside the magnetic shield unit. Therefore, it is possible
for the inside of the magnetic shield unit to be hardly influenced
by a magnetic field of the driving source. As a result, the
magnetic detection unit can perform measurement with less
noise.
Application Example 32
[0078] A living body magnetic field measurement method according to
this application example includes mounting a subject on a table;
causing a position measurement unit to measure a stereoscopic shape
of a measured surface of the subject; calculating a most protruding
portion of the stereoscopic shape; moving the table so that the
most protruding portion comes close to a magnetic detection unit
with a predetermined gap; and causing the magnetic detection unit
to detect a distribution of a magnetic vector in the subject.
[0079] According to this application example, the subject is
mounted on the table, and a stereoscopic shape of a measured
surface of the subject is measured. A most protruding portion of
the stereoscopic shape is calculated. Next, the table is moved so
that the most protruding portion comes close to the magnetic
detection unit with a predetermined gap. Successively, a
distribution of a magnetic vector in the subject is detected.
Therefore, the magnetic detection unit approaches and measures the
measured surface in a range in which the magnetic detection unit
does not come into contact with the measured surface. The position
measurement unit measures a position of the measured surface
relative to the magnetic detection unit, and then the table causes
the subject to come close to the magnetic detection unit. Thus,
even if the position measurement unit is separated from the
magnetic detection unit, the subject can be made to come close to
the magnetic detection unit. As a result, the living body magnetic
field measurement apparatus can measure a magnetic field of the
measured surface with high accuracy.
Application Example 33
[0080] In the living body magnetic field measurement method
according to the application example, in a case where the
stereoscopic shape is measured, a position of the subject in a
direction orthogonal to a longitudinal direction of the subject is
set, and, in a case where the table is moved, the table may be
moved in the longitudinal direction of the subject.
[0081] According to this application example, in a case where the
stereoscopic shape is measured, first, a position of the subject in
a direction orthogonal to a longitudinal direction of the subject
is set. Consequently, it is possible to reliably measure a
measurement region. Next, the table is moved in the longitudinal
direction of the subject. Consequently, it is possible to measure a
two-dimensional measurement region.
Application Example 34
[0082] In the living body magnetic field measurement apparatus
according to the application example, the magnetic shield unit may
have a tubular shape extending in the second direction, and the
tube may extend in the second direction along the magnetic shield
unit.
[0083] According to this application example, the tube extends in
the second direction, and the second direction is orthogonal to the
first direction. Therefore, a magnetic vector passing through the
tube hardly influences the magnetic detection unit. As a result,
the magnetic detection unit can perform measurement with less
noise. Since the tube is provided along the magnetic shield unit,
the tube is easily fixed to the magnetic shield unit. Thus, it is
possible to easily provide the tube.
BRIEF DESCRIPTION OF THE DRAWINGS
[0084] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0085] FIG. 1 is a schematic perspective view illustrating a
configuration of a magnetic field measurement apparatus according
to a first embodiment.
[0086] FIG. 2A is a schematic side sectional view for explaining a
structure of a shape measurement device, and FIG. 2B is a schematic
side view for explaining a structure of the shape measurement
device.
[0087] FIG. 3A is a main portion schematic plan view for explaining
an arrangement of a tilting device, and FIG. 3B is a schematic side
sectional view for explaining a structure of the shape measurement
device.
[0088] FIG. 4 is a main portion schematic perspective view
illustrating a positional relationship between a measured surface
and a magnetic sensor.
[0089] FIG. 5A is a schematic side view illustrating a structure of
an attachment/detachment portion; FIG. 5B is a side view of a
grooved rod; FIG. 5C is a side view of a grooved cylinder; and FIG.
5D is a schematic side view illustrating a structure of the
attachment/detachment portion.
[0090] FIG. 6A is a schematic side view illustrating a structure of
the magnetic sensor, and FIG. 6B is a schematic plan view
illustrating a structure of the magnetic sensor.
[0091] FIG. 7 is an electrical control block diagram of a
controller.
[0092] FIG. 8 is a flowchart illustrating a magnetic field
measurement method.
[0093] FIGS. 9A to 9C are schematic diagrams for explaining the
magnetic field measurement method.
[0094] FIGS. 10A to 10C are schematic diagrams for explaining the
magnetic field measurement method.
[0095] FIGS. 11A and 11B are schematic diagrams for explaining the
magnetic field measurement method.
[0096] FIGS. 12A to 12C are schematic diagrams for explaining the
magnetic field measurement method.
[0097] FIG. 13 is a schematic perspective view illustrating a
configuration of a living body magnetic field measurement apparatus
according to a second embodiment.
[0098] FIG. 14A is a schematic side view illustrating a structure
of a contour measurement section, and FIG. 14B is a schematic top
view illustrating a structure of the contour measurement
section.
[0099] FIGS. 15A and 15B are schematic sectional views illustrating
a structure of the table.
[0100] FIG. 16A is a side view illustrating a structure of an
X-direction table; FIG. 16B is a main portion schematic enlarged
view for explaining a movable range of the division surface; FIG.
16C is a top sectional view for explaining a configuration of a
tube; and FIG. 16D is a side sectional view for explaining a
configuration of the tube.
[0101] FIG. 17A is a schematic side view illustrating a structure
of a magnetic sensor, and FIG. 17B is a schematic plan view
illustrating a structure of the magnetic sensor.
[0102] FIG. 18 is an electrical control block diagram of a
controller.
[0103] FIG. 19 is a flowchart illustrating a living body magnetic
field measurement method.
[0104] FIGS. 20A to 20E are schematic diagrams for explaining the
living body magnetic field measurement method.
[0105] FIGS. 21A to 21C are schematic diagrams for explaining the
living body magnetic field measurement method.
[0106] FIGS. 22A and 22B are schematic diagrams for explaining the
living body magnetic field measurement method.
[0107] FIG. 23 is a schematic perspective view illustrating a
configuration of a living body magnetic field measurement apparatus
according to a fourth embodiment.
[0108] FIGS. 24A and 24B are schematic sectional views for
explaining a structure of the position measurement device.
[0109] FIG. 25A is a perspective view of a three-dimensional image
measured by the position measurement device, and FIG. 25B is a
schematic side view of a stereoscopic image for explaining
measurement in the position measurement device.
[0110] FIGS. 26A and 26B are schematic side sectional views
illustrating a structure of the table.
[0111] FIG. 27A is a schematic side view illustrating a structure
of an attachment/detachment portion; FIG. 27B is a side view of a
grooved rod; FIG. 27C is a side view of a grooved cylinder; and
FIG. 27D is a schematic side view illustrating a structure of the
attachment/detachment portion.
[0112] FIG. 28A is a top sectional view for explaining a
configuration of a tube, and FIG. 28B is a side sectional view for
explaining a configuration of the tube.
[0113] FIG. 29A is a schematic side view illustrating a structure
of a magnetic sensor, and FIG. 29B is a schematic plan view
illustrating a structure of the magnetic sensor.
[0114] FIG. 30 is an electrical control block diagram of a
controller.
[0115] FIG. 31 is a flowchart illustrating a living body magnetic
field measurement method.
[0116] FIGS. 32A to 32C are schematic diagrams for explaining the
living body magnetic field measurement method.
[0117] FIGS. 33A to 33C are schematic diagrams for explaining the
living body magnetic field measurement method.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0118] In the present embodiments, with reference to the drawings,
a description will be made of characteristic examples of a magnetic
field measurement apparatus and a magnetic field measurement method
of measuring a heart magnetic field generated from the heart by
using the magnetic field measurement apparatus. In addition,
respective members in the drawings are illustrated in different
scales in order to be recognizable in the drawings.
First Embodiment
[0119] With reference to FIGS. 1 to 7, a description will be made
of a structure of a magnetic field measurement apparatus according
to a first embodiment. FIG. 1 is a schematic perspective view
illustrating a configuration of the magnetic field measurement
apparatus. As illustrated in FIG. 1, a magnetic field measurement
apparatus 1 mainly includes an electromagnetic shield device 2 as a
magnetic shield unit, a table 3 as a movable table, a magnetic
sensor 4 as a detection unit, and a shape measurement device 5 as a
position measurement unit, a guide light irradiation unit, and a
measurement unit.
[0120] The electromagnetic shield device 2 includes a rectangular
tubular main body 2a. A longitudinal direction of the main body 2a
is set to a Y direction. The gravity direction is set to a -Z
direction, and a direction orthogonal to the Y direction and the Z
direction is set to an X direction. The electromagnetic shield
device 2 prevents an external magnetic field such as terrestrial
magnetism from entering a space where the magnetic sensor 4 is
disposed. In other words, the electromagnetic shield device 2
attenuates a magnetic force line entering the inside. That is, the
influence of the external magnetic field on the magnetic sensor 4
is minimized by the electromagnetic shield device 2, and a magnetic
field in the location where the magnetic sensor 4 is present is
considerably lower than the external magnetic field. The main body
2a extends in the Y direction, and the main body 2a functions as a
passive magnetic shield. The inside of the main body 2a is hollow,
and a sectional shape of surfaces passing through the X direction
and the Z direction is a substantially quadrangle shape. The
surfaces passing through the X direction and the Z direction
indicate orthogonal planes orthogonal in the Y direction in the XZ
section.
[0121] A sectional shape of the main body 2a is a square shape. The
electromagnetic shield device 2 is provided with an opening 2b on
the -Y direction side, and the table 3 protrudes out of the opening
2b. The size of the electromagnetic shield device 2 is not
particularly limited, but, in the present embodiment, for example,
a length thereof in the Y direction is about 200 cm, and one side
of the opening 2b is about 90 cm. A subject 6 mounted on the table
3 can come in and out of the electromagnetic shield device 2 via
the opening 2b along with the table 3. In the present embodiment,
the subject 6 is a human, but an animal other than a human may be
used as the subject 6. A door 2d is provided in the opening 2b via
so as to be opened and closed via hinges. The opening 2b may be
closed by the door 2d after the subject 6 and the table 3 enter the
main body 2a. The door 2d can reduce a magnetic field entering the
main body 2a.
[0122] The main body 2a and the door 2d are made of a ferromagnetic
material having relative permeability of, for example, several
thousands or more, or a conductor having high conductivity. As the
ferromagnetic material, permalloy, ferrite, iron, chromium,
cobalt-based amorphous metal, or the like may be used. As the
conductor having high conductivity, for example, aluminum which has
a magnetic field reduction function due to an eddy current effect
may be used. The main body 2a may be formed by alternately stacking
a ferromagnetic material and a conductor having high conductivity.
In the present embodiment, for example, each of the main body 2a
and the door 2d is formed by alternately staking an aluminum plate
and a permalloy plate as two layers whose entire thickness is about
20 mm to 30 mm.
[0123] First Helmholtz coils 2c are provided at ends on the +Y
direction side and the -Y direction side of the main body 2a. The
first Helmholtz coils 2c are coils for correcting an entering
magnetic field which enters the internal space of the main body 2a.
The entering magnetic field indicates an external magnetic field
which passes through the opening 2b and enters the internal space.
The entering magnetic field is strongest with respect to the
opening 2b in the Y direction. The first Helmholtz coils 2c
generate a magnetic field which cancels out the entering magnetic
field by using a current.
[0124] The table 3 is provided with a foundation 7. The foundation
7 is disposed on the bottom inside the main body 2a, and extends
from the inside of the main body 2a to the outside of the opening
2b through the opening 2b in the Y direction. The foundation 7
extends in a direction in which the subject 6 is movable. A pair of
Y-direction rails 8 extending in the Y direction is provided on the
foundation 7. A Y-direction table 9 which is moved in the Y
direction as a second direction 9a along the Y-direction rails 8 is
provided on the Y-direction rails 8. A Y-direction linear motion
mechanism 10 which moves the Y-direction table 9 is provided
between the two Y-direction rails 8.
[0125] A Z-direction table 11 is provided on the Y-direction table
9, and a lifting device (not illustrated) is provided between the
Y-direction table 9 and the Z-direction table 11. The lifting
device lifts the Z-direction table 11. Six X-direction rails 12
extending in the X direction are provided on a surface on the +Z
direction side of the Z-direction table 11. An X-direction table 13
which is moved in the X direction along the X-direction rails 12 is
provided on the X-direction rails 12.
[0126] An X-direction linear movement mechanism 14 which moves the
X-direction table 13 in the X direction as a third direction 13d is
provided on the -Y direction side on the Z-direction table 11. The
X-direction linear movement mechanism 14 includes a pair of bearing
portions 14a, and the bearing portions 14a are provided to be erect
on the Z-direction table 11. The X-direction table 13 is located
between the two bearing portions 14a. The two bearing portions 14a
rotatably support a first screw rod 14b. A first penetration hole
(not illustrated) which penetrates in the X direction is provided
in the X-direction table 13, and the first screw rod 14b is
provided to penetrate through the first penetration hole of the
X-direction table 13. A female screw (not illustrated) is formed on
the first penetration hole, and the first screw rod 14b is engaged
with the female screw.
[0127] An attachment/detachment portion 15 is provided at one end
on the -X direction side of the first screw rod 14b, and the
attachment/detachment portion 15 is fixed to the first screw rod
14b. If the attachment/detachment portion 15 is rotated, the first
screw rod 14b is rotated. Since the first screw rod 14b is engaged
with the female screw of the X-direction table 13, if the first
screw rod 14b is rotated, the X-direction table 13 is moved in the
X direction. The attachment/detachment portion 15 is coupled to a
rotation shaft of an X-direction table motor 16. The X-direction
table motor 16 rotates the attachment/detachment portion 15 so as
to move the X-direction table 13 in the X direction. The
X-direction table motor 16 is coupled to a motor movement portion
17 which moves the X-direction table motor 16 in the X direction.
The X-direction linear movement mechanism 14 is constituted of the
bearing portions 14a, the first screw rod 14b, the
attachment/detachment portion 15, the X-direction table motor 16,
the motor movement portion 17, and the like.
[0128] A tilting table 18 is provided over the X-direction table
13, and a tilting device (not illustrated) is provided between the
X-direction table 13 and the tilting table 18. The tilting device
tilts the tilting table 18 with respect to the X-direction table
13. The foundation 7, the Y-direction rails 8, the Y-direction
table 9, the Y-direction linear motion mechanism 10, the
Z-direction table 11, the X-direction rails 12, the X-direction
table 13, the bearing portions 14a, the first screw rod 14b, and
the tilting table 18 constituting the table 3 are made of
non-magnetic materials such as a wood, a resin, a ceramic, and
non-magnetic metal. A portion of the table 3 which is moved to the
inside of the electromagnetic shield device 2 is made of a
non-magnetic material. Consequently, it is possible to prevent
magnetization of the table 3 from influencing measurement of a
magnetic field.
[0129] In the electromagnetic shield device 2, the shape
measurement device 5 is provided on the +Z direction side of the
opening 2b. The shape measurement device 5 is a device used to
position the subject 6 or measure a surface shape. The subject 6
mounted on the table 3 passes through the opening 2b. The subject 6
passes near the shape measurement device 5, and thus the shape
measurement device 5 can easily irradiate the subject 6 with light
beams. The shape measurement device 5 detects light reflected from
the subject 6 so as to measure a shape of the subject 6.
[0130] The magnetic sensor 4 is provided inside the electromagnetic
shield device 2. The magnetic sensor 4 is a sensor which detects a
magnetic field generated from the heart of the subject 6. The
magnetic sensor 4 is fixed to the electromagnetic shield device 2.
The location where the magnetic field measurement apparatus 1 is
disposed is adjusted to a state in which no magnetic field is
substantially present by the electromagnetic shield device 2.
Therefore, the magnetic sensor 4 can measure a magnetic field
generated from the heart without being influenced by noise. The
magnetic sensor 4 detects an intensity component of a magnetic
field in a first direction 4a which is the same direction as the Z
direction.
[0131] The first direction 4a and the second direction 9a are
directions orthogonal to each other. The first direction 4a and the
third direction 13d are directions orthogonal to each other. The
second direction 9a and the third direction 13d are also directions
orthogonal to each other. The table 3 moves the subject 6 in the
second direction 9a and the third direction 13d orthogonal to each
other. The table 3 is moved in an orthogonal coordinate system, and
can thus easily control a position of the subject 6. The table 3
controls a tilt angle of the subject 6. A direction in which the
electromagnetic shield device 2 extends is the second direction
9a.
[0132] A controller 21 is provided at a location separated from the
opening 2b. The controller 21 outputs an electric signal so as to
control the magnetic field measurement apparatus 1. Specifically,
the controller 21 controls the electromagnetic shield device 2, the
table 3, the magnetic sensor 4, and the shape measurement device 5.
A magnetic field or a residual magnetic field is generated due to
the electric signal of the controller 21, and becomes noise when
detected by the magnetic sensor 4. Since the controller 21 is
present at the location separated from the opening 2b, the magnetic
field or the residual magnetic field generated from the controller
21 hardly reaches the magnetic sensor 4. As a result, the magnetic
sensor 4 can perform measurement with less noise.
[0133] The controller 21 is provided with a display device 22 and
an input device 23. The display device 22 is a liquid crystal
display (LCD) or an organic light emitting diode (OLED). A
measurement situation, a measurement result, and the like are
displayed on the display device 22. The input device 23 is
constituted of a keyboard, a rotary knob, or the like. An operator
operates the input device 23 so as to input various instructions
such as a measurement starting instruction or a measurement
condition to the magnetic field measurement apparatus 1.
[0134] FIG. 2A is a schematic sectional view for explaining a
structure of the shape measurement device, and is a view taken
along the side surface of the electromagnetic shield device 2. FIG.
2B is a schematic sectional view for explaining a structure of the
shape measurement device, and is a view in which the magnetic field
measurement apparatus 1 is viewed from the -Y direction side. In
FIGS. 2A and 2B, the shape measurement device 5 includes a laser
scanning unit 5a and an imaging device 5b as a guide light
irradiation unit. The laser scanning unit 5a is provided on a
ceiling of the main body 2a in the opening 2b, and emits laser
light 5c as light and a light beam in the -Z direction. A front
face 6a of the subject 6 is irradiated with the laser light 5c. The
laser light 5c is reflected from the front face 6a. The laser
scanning unit 5a has a function of performing scanning with the
laser light 5c in the X direction, and a function of irradiating a
single point without scanning. When the laser scanning unit 5a
performs scanning with the laser light 5c, a reflection point 5d at
which the laser light 5c is reflected from the front face 6a is
linear when viewed from the imaging device 5b. When the laser
scanning unit 5a does not perform scanning with the laser light 5c,
the reflection point 5d at which the laser light 5c is reflected
from the front face 6a is a single point.
[0135] When the subject 6 is positioned, the subject 6 is mounted
on the table 3 so as to be directed upward. The laser scanning unit
5a irradiates the chest of the subject 6 without scanning with the
laser light 5c. The operator drives the Y-direction linear motion
mechanism 10 so as to move the Y-direction table 9 in the Y
direction. The operator drives the X-direction linear movement
mechanism 14 and the X-direction table motor 16 so as to move the
X-direction table 13 in the X direction. Positions of the table 3
in the X direction and the Y direction are adjusted so that the
laser light 5c is applied to the xiphisternum 6e of the subject
6.
[0136] The shape measurement device 5 has a function of applying
the laser light 5c as guide light, and a function of measuring a
position. The function of applying guide light is a function of
applying a light beam for guiding a position where the subject 6 is
mounted. The function of measuring a position is a function of
measuring a shape of the subject by irradiating the subject 6 with
a light beam. The shape measurement device 5 has the function of
applying guide light, and thus the shape measurement device 5
applies a light beam for guiding a position where the subject 6 is
mounted. Therefore, it is possible to reduce the number of
constituent elements compared with a case where the magnetic field
measurement apparatus 1 separately includes a constituent element
applying guide light and a constituent element measuring a
position.
[0137] The imaging device 5b is provided in the opening 2b of the
main body 2a via a support portion 5e. The imaging device 5b is
obliquely provided with respect to an advancing direction of the
laser light 5c. The imaging device 5b images reflected light 5f
which is reflected from the front face 6a of the subject 6. In this
case, the laser scanning unit 5a, the reflection point 5d, and the
imaging device 5b form a triangle. The distance between the laser
scanning unit 5a and the imaging device 5b is a known value. An
angle formed between the laser light 5c and the reflected light 5f
can be detected on the basis of an image captured by the imaging
device 5b. Therefore, the shape measurement device 5 can measure
the distance between the laser scanning unit 5a and the reflection
point 5d by using a triangulation method. As mentioned above, the
shape measurement device 5 irradiates the subject 6 with the laser
light 5c so as to measure a location irradiated with the laser
light 5c. A surface of the subject 6 is uneven, and the laser light
5c is reflected at the uneven surface. Therefore, the shape
measurement device 5 can easily detect a surface shape of the
subject 6 by detecting a position of the laser light 5c reflected
from the subject 6.
[0138] The pair of first Helmholtz coils 2c is provided at the
foundation 7. A shape of each of the first Helmholtz coils 2c is a
quadrangle frame shape, and the first Helmholtz coils 2c are
disposed to surround the main body 2a. A part of the first
Helmholtz coil 2c on the -Z direction side is located in the inner
part of the foundation 7. The main body 2a is installed inside the
first Helmholtz coils 2c. Consequently, the first Helmholtz coils
2c have a structure of surrounding the main body 2a over the entire
circumference thereof.
[0139] The Y-direction linear motion mechanism 10 includes a motor
10a as a driving source. A first pulley 10b is provided on a
rotation shaft of the motor 10a, and a second pulley 10c is
rotatably provided at an end on the Y direction side of the
Y-direction linear motion mechanism 10. A timing belt 10d is hung
on the first pulley 10b and the second pulley 10c. A connection
portion 10e is provided on the timing belt 10d, and the connection
portion 10e connects the timing belt 10d to the Y-direction table
9. When the motor 10a rotates the first pulley 10b, the connection
portion 10e is moved in the Y direction by the torque of the motor
10a. The Y-direction table 9 is moved due to the movement of the
connection portion 10e. Therefore, the motor 10a can move the
Y-direction table 9 in the Y direction. The motor 10a changes a
rotation direction of the first pulley 10b so as to move the
Y-direction table 9 in both directions such as +Y direction and the
-Y direction.
[0140] Materials of the Y-direction rails 8, the second pulley 10c,
the timing belt 10d, and the connection portion 10e are
non-magnetic materials. The timing belt 10d is made of rubber and
resin. The Y-direction rails 8, the second pulley 10c, and the
connection portion 10e are made of ceramics. Therefore, a portion
of the Y-direction linear motion mechanism 10 entering the
electromagnetic shield device 2 is non-magnetic.
[0141] Four lifting devices 24 are provided side by side in the Y
direction in the Y-direction table 9. Each of the lifting devices
24 has a structure in which three air cylinders are arranged in the
X direction. The lifting device 24 expands and contracts the air
cylinders so as to lift the Z-direction table 11 in the first
direction 4a. Each air cylinder is provided with a length
measurement device (not illustrated), and thus the lifting device
24 detects a movement amount of the Z-direction table 11. The
respective air cylinders move the Z-direction table 11 by the same
distance, and thus the lifting devices 24 can move the Z-direction
table 11 in parallel. Pneumatic equipment such as a compressor and
an electromagnetic valve (not illustrated) is provided in the
controller 21. The lifting devices 24 are controlled by the
controller 21. The Y-direction table 9, the lifting devices 24, and
the Z-direction table 11 are made of aluminum. Therefore, the
Y-direction table 9, the lifting devices 24, and the Z-direction
table 11 are non-magnetic.
[0142] The X-direction table 13 is provided with wheels 25 which
are in contact with the X-direction rails 12. The wheels 25 are
rotated, and thus the X-direction table 13 can be easily moved in
the X direction. The X-direction table 13, the X-direction rails
12, and the wheels 25 are made of ceramics which are non-magnetic
materials. Therefore, the X-direction table 13, the X-direction
rails 12, and the wheels 25 are non-magnetic. A portion of the
table 3 entering the electromagnetic shield device 2 is
non-magnetic. Consequently, it is possible to prevent magnetization
of the table 3 from influencing measurement of a magnetic
field.
[0143] A tilting device 26 as a leg portion is provided between the
X-direction table 13 and the tilting table 18. The tilting device
26 includes a first tilting portion 26a, a second tilting portion
26b, and a third tilting portion 26c. The first tilting portion 26a
to the third tilting portion 26c have the same structure as that of
the lifting device 24. The controller 21 controls a length of
expansion/contraction of each of the first tilting portion 26a to
the third tilting portion 26c. An X-direction table 13 side of the
first tilting portion 26a is fixed to the X-direction table 13. The
first tilting portion 26a on a tilting table 18 side has a conical
shape, and is coupled to the tilting table 18 via a pivot
bearing.
[0144] Both of an X-direction table 13 side and a tilting table 18
side of each of the second tilting portion 26b and the third
tilting portion 26c have a conical shape. The second tilting
portion 26b and the third tilting portion 26c are coupled to the
X-direction table 13 and the tilting table 18 via pivot bearings.
FIG. 3A is a main portion schematic plan view for explaining
arrangement of the tilting device. As illustrated in FIG. 3A, the
first tilting portion 26a is provided on the +Y direction side of
the tilting table 18. The second tilting portion 26b is provided on
the -X direction side of the -Y direction side of the tilting table
18. The third tilting portion 26c is provided on the +X direction
side of the -Y direction side of the tilting table 18. A line
connecting the first tilting portion 26a to the third tilting
portion 26c to each other forms an isosceles triangle.
[0145] When the first tilting portion 26a is expanded or
contracted, the tilting table 18 is rotated with a line connecting
the second tilting portion 26b to the third tilting portion 26c as
an axis. When the second tilting portion 26b is expanded or
contracted, the tilting table 18 is rotated with a line connecting
the first tilting portion 26a to the third tilting portion 26c as
an axis. When the third tilting portion 26c is expanded or
contracted, the tilting table 18 is rotated with a line connecting
the first tilting portion 26a to the second tilting portion 26b as
an axis. The controller 21 controls an expansion/contraction amount
of each of the first tilting portion 26a to the third tilting
portion 26c so as to control a tilt angle of the tilting table 18.
In other words, the controller 21 controls lengths of the first
tilting portion 26a to the third tilting portion 26c so as to tilt
the subject 6.
[0146] As one of structures of a device tilting the tilting table
18, there is a structure in which a tilting device controlling a
tilt is provided at the center of the tilting table 18. On the
other hand, in the table 3 of the present embodiment, the first
tilting portion 26a to the third tilting portion 26c have a
structure of supporting the tilting table 18. When compared with
the structure in which the tilting device is provided at the
center, loads of the tilting table 18 and the subject 6 can be
distributed to the first tilting portion 26a to the third tilting
portion 26c in the table 3, and thus it is possible to control a
tilt of the tilting table 18 with a lightweight structure.
[0147] Referring to FIGS. 2A and 2B again, the magnetic sensor 4 is
provided on the ceiling of the main body 2a via a support member
27. A position of the center of the magnetic sensor 4 in the Z
direction is the central position between the ceiling of the main
body 2a and the bottom of the main body 2a. A position of the
center of the magnetic sensor 4 in the X direction is the central
position between a wall on the +X direction side of the main body
2a and a wall on the -X direction side thereof. The distance
between the center of the magnetic sensor 4 in the Y direction and
an end on the -Y direction side of the main body 2a is the same as
the distance between the center of the magnetic sensor 4 and the
wall on the +Y direction side of the main body 2a. When the center
of the magnetic sensor 4 is located at this location, it is
possible for the magnetic sensor 4 to be hardly influenced by a
magnetic field which enters the electromagnetic shield device 2
from the outside thereof.
[0148] A second Helmholtz coil 28 having a cube frame shape is
provided inside the electromagnetic shield device 2. Specifically,
at least three correction coils are provided in the second
Helmholtz coil 28 so as to be orthogonal to each other in the X
direction, the Y direction, and the Z direction. In an X-direction
correction coil 28a orthogonal to the X direction, a measurement
space in which the subject 6 is disposed during measurement and the
magnetic sensor 4 are interposed between a pair of coils from the X
direction. The X-direction correction coil 28a generates a magnetic
field in the X direction and cancels out an external magnetic field
in the X direction so that an X component of a magnetic field of
the measurement space and the space in which the magnetic sensor 4
is disposed is reduced to the extent or less of not having an
adverse effect on measurement.
[0149] Two pairs of coils are provided in a Y-direction correction
coil 28b orthogonal to the Y direction, and the measurement space
and the magnetic sensor 4 are interposed between the coils of the
Y-direction correction coil 28b from the Y direction. The
Y-direction correction coil 28b includes two pairs of coils, and
thus includes four coils. The Y-direction correction coil 28b
generates a magnetic field in the Y direction and cancels out an
external magnetic field in the Y direction so that a Y component of
a magnetic field of the measurement space and the space in which
the magnetic sensor 4 is disposed is reduced to the extent or less
of not having an adverse effect on measurement. The main body 2a
has a tubular shape extending in the Y direction, and an entering
magnetic field is considerable in the Y direction. For this reason,
the Y-direction correction coil 28b includes the two pairs of
coils.
[0150] In a Z-direction correction coil 28c orthogonal to the Z
direction, a measurement space in which the subject 6 is disposed
during measurement and the magnetic sensor 4 are interposed between
a pair of coils from the Z direction. The Z-direction correction
coil 28c generates a magnetic field in the Z direction and cancels
out an external magnetic field in the Z direction so that a Z
component of a magnetic field of the measurement space and the
space in which the magnetic sensor 4 is disposed is reduced to the
extent or less of not having an adverse effect on measurement.
[0151] The second Helmholtz coil 28 has a square frame shape when
viewed from each orthogonal direction side, and is disposed so that
the central position of the square frame overlaps the central
position of the magnetic sensor 4. A length of the side of the
square is not particularly limited, but, in the present embodiment,
a length of one side is equal to or more than 75 cm and equal to or
less than 85 cm. In FIGS. 2A and 2B, the shape of the second
Helmholtz coil 28 is a rectangular shape for better viewing, but is
actually a square shape.
[0152] In the Y-direction correction coil 28b, the four coils are
disposed at the same interval in the Y direction. When viewed from
the X direction, an outer circumference of the second Helmholtz
coil 28 has a square frame shape, and there is a structure in which
two coils are disposed inside the square frame shape. The second
Helmholtz coil 28 is disposed so that the central position of the
square frame shape overlaps the central position of the magnetic
sensor 4.
[0153] A shape of the second Helmholtz coil 28 viewed from the Z
direction is a square frame shape which is the same as the shape
viewed from the X direction. The second Helmholtz coil 28 is
disposed so that the central position of the square frame shape
overlaps the central position of the magnetic sensor 4. The second
Helmholtz coil 28 has such a shape, and thus it is possible to
further reduce a disturbance magnetic field in the magnetic sensor
4. Particularly, it is possible to reduce the influence of a
magnetic flux which comes from the -Y direction side of the
electromagnetic shield device 2.
[0154] When the table 3 is located on the -Y direction side of the
electromagnetic shield device 2, a half or more of the table 3
protrudes out of the electromagnetic shield device 2. Consequently,
the subject 6 is easily mounted on the table 3. When the subject 6
is mounted on the table 3, a height from the floor to the nose of
the subject 6 is smaller than a height from the floor to the
surface on the -Z direction side of the magnetic sensor 4.
Therefore, when the Y-direction table 9 is moved in the Y
direction, the subject 6 does not interfere with the magnetic
sensor 4.
[0155] FIG. 3B a schematic side sectional view for explaining a
structure of the shape measurement device, and illustrates a state
in which the table 3 is moved into the electromagnetic shield
device 2, and a heart magnetic field of the subject 6 is being
measured. As illustrated in FIG. 3B, the Y-direction table 9 is
moved in the +Y direction, and then the Z-direction table 11 is
moved up. A distance by which the Z-direction table 11 is moved up
is calculated by the controller 21.
[0156] FIG. 4 is a main portion schematic perspective view
illustrating a positional relationship between a measurement
surface and the magnetic sensor. As illustrated in FIG. 4, a
location measured by the magnetic sensor 4 on a surface of the
chest 6c of the subject 6 is a measured surface 6d as a measured
portion. In this case, the measured surface 6d is located at a
location opposing the magnetic sensor 4, and comes close to the
magnetic sensor 4. A surface which opposes the measured surface 6d
in the magnetic sensor 4 is referred to as an opposing surface 4e
or a first surface 4e. The controller 21 controls the table 3 so
that the distance between the measured surface 6d and the magnetic
sensor 4 becomes 5 mm as a predetermined distance. The measured
surface 6d is measured by the magnetic sensor 4. The measured
surface 6d is a surface opposing the heart 6g, and the magnetic
sensor 4 detects a magnetic field generated from the heart 6g. A
magnetic field generated due to an activity of the heart 6g is
output from the surface of the chest 6c. As a result, the magnetic
sensor 4 can detect the activity of the heart 6g.
[0157] FIG. 5A is a schematic side view illustrating a structure of
the attachment/detachment portion, and illustrates a separation
state in which the attachment/detachment portion 15 is separated.
As illustrated in FIG. 5A, an attachment/detachment portion
installation stand 29 is on the -X direction side of the foundation
7. The motor movement portion 17 is provided at an end on the -X
direction side on the attachment/detachment portion installation
stand 29. The motor movement portion 17 is constituted of a motor
17a, a screw rod 17b, guide rails 17c, and the like. The motor 17a
is provided on the -X direction side of the attachment/detachment
portion installation stand 29, and the guide rails 17c are provided
on the +X direction side of the motor 17a. The guide rails 17c are
provided as a pair, and extend in the X direction.
[0158] The X-direction table motor 16 is provided on the guide
rails 17c, and the X-direction table motor 16 is reciprocally moved
along the guide rails 17c. A rotation shaft of the motor 17a is
provided with the screw rod 17b extending in the X direction. A
penetration hole 16a extending in the X direction is provided in
the X-direction table motor 16, and a female screw is formed on the
penetration hole 16a. The female screw of the penetration hole 16a
is screwed with the screw rod 17b. When the motor 17a rotates the
screw rod 17b, the X-direction table motor 16 is moved in the X
direction along the guide rails 17c. A rotation shaft of the
X-direction table motor 16 is provided with a grooved cylinder 15a.
A grooved rod 15b is provided at an end on the -X direction side of
the first screw rod 14b. When the X-direction table motor 16 is
moved in the X direction, the grooved rod 15b is inserted into the
grooved cylinder 15a.
[0159] FIG. 5B is a side view of the grooved rod, and is a view in
which the grooved rod 15b is viewed from an axial direction. As
illustrated in FIG. 5B, grooves are provided on an outer
circumference of the grooved rod 15b. FIG. 5C is a side view of the
grooved cylinder, and is a view in which the grooved cylinder 15a
is viewed from an axial direction. As illustrated in FIG. 5C,
grooves extending in the axial direction are provided on an inner
diameter of the grooved cylinder 15a. An outer circumference shape
of the grooved rod 15b is substantially the same as an inner
circumference shape of the grooved cylinder 15a. When the grooved
rod 15b is inserted into the grooved cylinder 15a, the grooves of
the grooved cylinder 15a mesh with the grooves of the grooved rod
15b. Consequently, the torque applied to the grooved cylinder 15a
is transmitted to the grooved rod 15b.
[0160] FIG. 5D is a schematic side view illustrating a structure of
the attachment/detachment portion, and illustrates a connection
state of the attachment/detachment portion 15. In FIG. 5D, the
motor movement portion 17 moves the X-direction table motor 16 in
the X direction, and thus the grooved rod 15b is inserted into the
grooved cylinder 15a. When the X-direction table motor 16 rotates
the rotation shaft, the grooved rod 15b is rotated due to rotation
of the grooved cylinder 15a. Therefore, when the X-direction table
motor 16 rotates the rotation shaft, the first screw rod 14b
coupled to the grooved rod 15b is rotated. The X-direction table
motor 16 moves the X-direction table 13 in the X direction.
[0161] FIG. 6A is a schematic side view illustrating a structure of
the magnetic sensor, and FIG. 6B is a schematic plan view
illustrating a structure of the magnetic sensor. As illustrated in
FIGS. 6A and 6B, laser light 31 is supplied from a laser light
source 30 to the magnetic sensor 4. The laser light source 30 is
provided in the controller 21, and the laser light 31 is supplied
to the magnetic sensor 4 through an optical fiber 32. The magnetic
sensor 4 is coupled to the optical fiber 32 via an optical
connector 33.
[0162] The laser light source 30 outputs the laser light 31 with a
wavelength corresponding to an absorption line of cesium. A
wavelength of the laser light 31 is not particularly limited, but
is set to a wavelength of 894 nm corresponding to the D1-line, in
the present embodiment. The laser light source 30 is a tunable
laser device, and the laser light 31 output from the laser light
source 30 is continuous light with a predetermined light
amount.
[0163] The laser light 31 supplied via the optical connector 33
travels in the +X direction and is applied to a polarization plate
34. The laser light 31 having passed through the polarization plate
34 is linearly polarized. The laser light 31 is sequentially
applied to a first half mirror 35, a second half mirror 36, a third
half mirror 37, and a first reflection mirror 38. Some of the laser
light 31 is reflected by the first half mirror 35, the second half
mirror 36, and the third half mirror 37 so as to travel in the -Y
direction. The other light is transmitted therethrough so as to
travel in the +X direction. The first reflection mirror 38 reflects
the entire incident laser light 31 in the -Y direction. An optical
path of the laser light 31 is divided into four optical paths by
the first half mirror 35, the second half mirror 36, the third half
mirror 37, and the first reflection mirror 38. Reflectance of each
mirror is set so that light intensities of the laser light beams 31
on the respective optical paths are the same as each other.
[0164] Next, the laser light 31 is sequentially applied to a fourth
half mirror 41, a fifth half mirror 42, a sixth half mirror 43, and
a second reflection mirror 44. Some of the laser light 31 is
reflected by the fourth half mirror 41, the fifth half mirror 42,
and the sixth half mirror 43 so as to travel in the +Z direction.
The other light 31 is transmitted therethrough so as to travel in
the -Y direction. The second reflection mirror 44 reflects the
entire incident laser light 31 in the +Z direction. A single
optical path of the laser light 31 is divided into four optical
paths by the fourth half mirror 41, the fifth half mirror 42, the
sixth half mirror 43, and the second reflection mirror 44.
Reflectance of each mirror is set so that light intensities of the
laser light beams 31 on the respective optical paths are the same
as each other. Therefore, the optical path of the laser light 31 is
divided into the sixteen optical paths. In addition, reflectance of
each mirror is set so that light intensities of the laser light
beams 31 on the respective optical paths are the same as each
other.
[0165] Gas cells 45 are provided on the respective optical paths of
the laser light 31 on the +Z direction side of the fourth half
mirror 41, the fifth half mirror 42, the sixth half mirror 43, and
the second reflection mirror 44. The number of gas cells 45 is 16
in four rows and four columns. The laser light beams 31 reflected
by the fourth half mirror 41, the fifth half mirror 42, the sixth
half mirror 43, and the second reflection mirror 44 pass through
the gas cells 45. The gas cell 45 is a box having a cavity therein,
and an alkali metal gas is enclosed in the cavity. The alkali metal
is not particularly limited, and potassium, rubidium, or cesium may
be used. In the present embodiment, for example, cesium is used as
the alkali metal.
[0166] A polarization separator 46 is provided on the +Z direction
side of each gas cell 45. The polarization separator 46 is an
element which separates the incident laser light 31 into two
polarization components of the laser light 31, which are orthogonal
to each other. As the polarization separator 46, for example, a
Wollaston prism or a polarized beam splitter may be used.
[0167] A first photodetector 47 is provided on the +Z direction
side of the polarization separator 46, and a second photodetector
48 is provided on the -Y direction side of the polarization
separator 46. The laser light 31 having passed through the
polarization separator 46 is applied to the first photodetector 47,
and the laser light 31 reflected by the polarization separator 46
is applied to the second photodetector 48. The first photodetector
47 and the second photodetector 48 output signals corresponding to
an amount of incident laser light 31 to the controller 21. If the
first photodetector 47 and the second photodetector 48 generate
magnetic fields, this may influence measurement, and thus it is
preferable that the first photodetector 47 and the second
photodetector 48 are made of a non-magnetic material. The magnetic
sensor 4 includes heaters 49 which are provided on both sides in
the X direction and both sides in the Y direction. Each of the
heaters 49 preferably has a structure in which a magnetic field is
not generated, and may employ, for example, a heater of a type of
performing heating by causing steam or hot air to pass through a
flow passage. Instead of using a heater, the gas cell 45 may be
inductively heated by using a high frequency voltage.
[0168] The magnetic sensor 4 is disposed on the +Z direction side
of the subject 6. A magnetic vector 50 as a magnetic field
generated from the subject 6 enters the magnetic sensor 4 from the
-Z direction side. The magnetic vector 50 passes through the fourth
half mirror 41 to the second reflection mirror 44, and then passes
through the gas cell 45. The magnetic vector 50 passes through the
polarization separator 46, and comes out of the magnetic sensor
4.
[0169] The magnetic sensor 4 is a sensor which is called an optical
pumping type magnetic sensor or an optical pumping atom magnetic
sensor. Cesium in the gas cell 45 is heated and is brought into a
gaseous state. The cesium gas is irradiated with the linearly
polarized laser light 31, and thus cesium atoms are excited so that
orientations of magnetic moments can be aligned. When the magnetic
vector 50 passes through the gas cell 45 in this state, the
magnetic moments of the cesium atoms precess due to a magnetic
field of the magnetic vector 50. This precession is referred to as
Larmore precession. The magnitude of the Larmore precession has a
positive correlation with the strength of the magnetic vector 50.
In the Larmore precession, a polarization plane of the laser light
31 is rotated. The magnitude of the Larmore precession has a
positive correlation with a change amount of a rotation angle of
the polarization plane of the laser light 31. Therefore, the
strength of the magnetic vector 50 has a positive correlation with
the change amount of a rotation angel of the polarization plane of
the laser light 31. The magnetic sensor 4 has high sensitivity for
a component of the magnetic vector 50 in the first direction 4a,
and has low sensitivity for a component thereof orthogonal to the
first direction 4a.
[0170] The polarization separator 46 separates the laser light 31
into two components of linearly polarized light which are
orthogonal to each other. The first photodetector 47 and the second
photodetector 48 respectively detect the strengths of the two
components of linearly polarized light orthogonal to each other.
Consequently, the first photodetector 47 and the second
photodetector 48 can detect a rotation angle of a polarization
plane of the laser light 31. The magnetic sensor 4 can detect
strength of the magnetic vector 50 on the basis of a change of the
rotation angel of the polarization plane of the laser light 31. An
element constituted of the gas cell 45, the polarization separator
46, the first photodetector 47, and the second photodetector 48 is
referred to as a sensor element 4d. In the present embodiment,
sixteen sensor elements 4d of four rows and four columns are
disposed in the magnetic sensor 4. The number and arrangement of
the sensor elements 4d in the magnetic sensor 4 are not
particularly limited. The sensor elements 4d may be disposed in
three or less rows or five or more rows. Similarly, the sensor
elements 4d may be disposed in three or less columns or five or
more columns. The larger the number of sensor elements 4d, the
higher the spatial resolution.
[0171] FIG. 7 is an electrical control block diagram of the
controller. As illustrated in FIG. 7, the magnetic field
measurement apparatus 1 includes the controller 21 controlling an
operation of the magnetic field measurement apparatus 1. The
controller 21 includes a central processing unit (CPU) 51 which
performs various calculation processes as a processor, and a memory
52 which stores various information. A shape sensor driving device
53, a table driving device 54, the electromagnetic shield device 2,
a magnetic sensor driving device 55, the display device 22, and the
input device 23 are coupled to the CPU 51 via an input/output
interface 56 and a data bus 57.
[0172] The shape sensor driving device 53 is a device which drives
the laser scanning unit 5a and the imaging device 5b. The shape
sensor driving device 53 drives the laser scanning unit 5a to emit
the laser light 5c toward the subject 6. The shape sensor driving
device 53 performs scanning with the laser light 5c in the
horizontal direction. The shape sensor driving device 53 drives the
imaging device 5b to capture an image of the reflection point 5d.
In addition, the shape sensor driving device 53 irradiates a single
location without scanning with the laser light 5c. The irradiated
reflection point 5d is a guiding mark indicating a location where
the subject 6 is positioned.
[0173] The table driving device 54 is a device which drives the
X-direction table 13, the Y-direction table 9, the Z-direction
table 11, the tilting table 18, and the motor movement portion 17.
The table driving device 54 receives an instruction signal for
moving a position of the X-direction table 13 from the CPU 51. The
X-direction table 13 can be moved only when the Y-direction table 9
is located at a predetermined position. For this reason, first, the
Y-direction table 9 is moved to the predetermined position. The
table driving device 54 detects a position of the Y-direction table
9. The Y-direction table 9 includes a length measurement device
detecting a position thereof, and the length measurement device
detects a position of the Y-direction table 9. The table driving
device 54 moves the Y-direction table 9, and thus the Y-direction
table 9 is moved to a location where the grooved rod 15b opposes
the grooved cylinder 15a.
[0174] Next, the table driving device 54 drives the motor movement
portion 17 so that the grooved cylinder 15a is combined with the
grooved rod 15b. Successively, the table driving device 54 detects
a position of the X-direction table 13. The X-direction table 13
includes a length measurement device detecting a position thereof,
and the length measurement device detects a position of the
X-direction table 13. A difference between a position to which the
X-direction table 13 is scheduled to be moved and the present
position of the X-direction table 13 is calculated. The table
driving device 54 drives the X-direction table motor 16 to move the
X-direction table 13 to the position to which the X-direction table
13 is scheduled to be moved. Consequently, the table driving device
54 can move the X-direction table 13 to the location for which an
instruction is given. Successively, the table driving device 54
drives the motor movement portion 17 to separate the grooved
cylinder 15a from the grooved rod 15b.
[0175] Similarly, the table driving device 54 receives an
instruction signal for moving a position of the Y-direction table 9
from the CPU 51. The table driving device 54 detects a position of
the Y-direction table 9. A difference between a position to which
the Y-direction table 9 is scheduled to be moved and the present
position of the Y-direction table 9 is calculated. The table
driving device 54 drives the motor 10a to move the Y-direction
table 9 to the position to which the Y-direction table 9 is
scheduled to be moved. Consequently, the table driving device 54
can move the Y-direction table 9 between the position inside the
electromagnetic shield device 2 and the position outside the
electromagnetic shield device 2. In a case where the shape
measurement device 5 measures the chest 6c of the subject 6, the
Y-direction table 9 is moved at a constant speed.
[0176] Similarly, the table driving device 54 receives an
instruction signal for moving a position of the Z-direction table
11 from the CPU 51. Each of the lifting devices 24 lifting the
Z-direction table 11 includes a length measurement device detecting
position of the Z-direction table 11, and the table driving device
54 detects a position of the Z-direction table 11. A difference
between a position to which the Z-direction table 11 is scheduled
to be moved and the present position of the Z-direction table 11 is
calculated. The lifting device 24 is an air cylinder, and the table
driving device 54 is provided with pneumatic equipment such as a
compressor or an electromagnetic valve driving the lifting device
24. The table driving device 54 controls an amount of air supplied
to the lifting device 24 so as to move the Z-direction table 11 to
the position to which the Z-direction table 11 is scheduled to be
moved.
[0177] Similarly, the table driving device 54 receives an
instruction signal for tilting the tilting table 18 from the CPU
51. The tilting device 26 tilting the tilting table 18 includes a
length measurement device detecting a length of the tilting device
26. The table driving device 54 detects a tilt of the tilting table
18 by using the length of the tilting device 26 detected by the
length measurement device. A difference between an angle at which
the tilting table 18 is scheduled to be tilted and the present
angle of the tilting table 18 is calculated. The tilting device 26
is an air cylinder, and the table driving device 54 is provided
with pneumatic equipment such as a compressor or an electromagnetic
valve driving the tilting device 26. The table driving device 54
controls an amount of air supplied to the tilting device 26 so as
to tilt the tilting table 18 up to the angle at which the tilting
table 18 is scheduled to be tilted.
[0178] The electromagnetic shield device 2 includes the first
Helmholtz coil 2c and a sensor detecting an internal magnetic
field. The electromagnetic shield device 2 reduces an internal
magnetic field of the main body 2a by driving the first Helmholtz
coil 2c in response to an instruction from the CPU 51.
[0179] The magnetic sensor driving device 55 is a device driving
the magnetic sensor 4 and the laser light source 30. The magnetic
sensor 4 is provided with the first photodetector 47, the second
photodetector 48, and the heater 49. The magnetic sensor driving
device 55 drives the laser light source 30, the heater 49, the
first photodetector 47, and the second photodetector 48. The
magnetic sensor driving device 55 drives the laser light source 30
to supply the laser light 31 to the magnetic sensor 4. The magnetic
sensor driving device 55 drives the heater 49 so that the magnetic
sensor 4 is maintained at a predetermined temperature. The magnetic
sensor driving device 55 converts electric signals output from the
first photodetector 47 and the second photodetector 48 into digital
signals which are then output to the CPU 51.
[0180] The display device 22 displays predetermined information in
response to an instruction from the CPU 51. The operator operates
the input device 23 on the basis of the display content and inputs
the instruction content. The instruction content is transmitted to
the CPU 51.
[0181] The memory 52 is a concept including a semiconductor memory
such as a RAM or a ROM, a hard disk, and an external storage device
such as a DVD-ROM. In terms of a function, a storage region for
storing program software 58 in which control procedures of an
operation of the magnetic field measurement apparatus 1 are
described, or a storage region for storing measurement portion
shape data 61 which is data obtained by measuring a stereoscopic
shape of the measured surface 6d of the subject 6 is set. In
addition, a storage region for storing average plane data 62
obtained by calculating an average plane of the stereoscopic shape
of the measured surface 6d of the subject 6 on the basis of the
measurement portion shape data 61 is set. The average plane is a
plane passing through an average location of points on a surface of
the stereoscopic shape. Further, a storage region for storing table
movement amount data 63 which is data regarding movement amounts of
the X-direction table 13, the Y-direction table 9, and the
Z-direction table 11, and a tilt angle of the tilting table 18, is
set.
[0182] Still further, a storage region for storing magnetic sensor
related data 64 which is data such as parameters used to drive the
magnetic sensor 4 is set in the memory 52. Furthermore, a storage
region for storing magnetic measurement data 65 which is data
obtained by the magnetic sensor 4 measuring the measured surface 6d
is set in the memory 52. Moreover, a storage region functioning as
a work area for the CPU 51, a temporary file, or the like, and
other various storage regions are set.
[0183] The CPU 51 controls measurement of a magnetic field
generated from the heart of the subject 6 according to the program
software 58 stored in the memory 52. As a specific function
realizing unit, the CPU 51 includes a shape measurement control
unit 66 which is a measurement unit. The shape measurement control
unit 66 controls measurement of a stereoscopic shape of the
measured surface 6d of the subject 6 by driving the shape
measurement device 5 and the Y-direction table 9. The CPU 51
includes an average plane calculation unit 67 as a calculation
unit. The average plane calculation unit 67 calculates an average
plane by using a measurement result of the stereoscopic shape of
the subject 6.
[0184] The CPU 51 includes a table movement control unit 68 as a
control unit. The table movement control unit 68 controls movement
and stoppage positions of the X-direction table 13, the Y-direction
table 9, the Z-direction table 11, and the tilting table 18. The
CPU 51 includes an electromagnetic shield control unit 69. The
electromagnetic shield control unit 69 performs control for
minimizing a magnetic field around the magnetic sensor 4 by driving
the electromagnetic shield device 2.
[0185] The CPU 51 includes a magnetic sensor control unit 70. The
magnetic sensor control unit 70 performs control for causing the
magnetic sensor driving device 55 to drive the magnetic sensor 4 to
detect the strength of the magnetic vector 50. The CPU 51 includes
a laser pointer control unit 71. The laser pointer control unit 71
performs control for driving the laser scanning unit 5a to apply
the laser light 5c to only a single point of a predetermined
location.
[0186] In the present embodiment, the above-described respective
functions of the magnetic field measurement apparatus 1 are
realized in the program software by using the CPU 51, but, in a
case where the above-described respective functions can be realized
by hardware such as a stand-alone electronic circuit without using
the CPU 51, such an electronic circuit may be used.
[0187] Next, a description will be made of a magnetic field
measurement method using the above-described magnetic field
measurement apparatus 1 with reference to FIGS. 8 to 12C. FIG. 8 is
a flowchart illustrating a magnetic field measurement method. In
the flowchart illustrated in FIG. 8, step S1 is a subject mounting
step. In this step, the subject 6 is mounted on the tilting table
18. Next, the flow proceeds to step S2. Step S2 is a positioning
step. In this step, the laser scanning unit 5a irradiates one
location of the chest 6c with the laser light 5c. In this step, the
operator operates the input device 23 so that the X-direction table
13 and the Y-direction table 9 are moved, and thus the xiphisternum
6e of the subject 6 is irradiated with the reflection point 5d.
Next, the flow proceeds to step S3.
[0188] Step S3 corresponds to a measured surface shape measurement
step. In this step, the shape measurement control unit 66 drives
the Y-direction table 9 and the shape measurement device 5 to
measure a surface shape of the measured surface 6d of the subject
6. Next, the flow proceeds to step S4. Step S4 is an average plane
calculation step. In this step, the average plane calculation unit
67 calculates an average plane by using data regarding the measured
surface shape. Next, the flow proceeds to step S5.
[0189] Step S5 is a table movement step. In this step, the table
movement control unit 68 moves the table 3 and tilts the tilting
table 18 so that the average plane of the measured surface 6d
becomes parallel to the opposing surface 4e. The chest 6c of the
subject 6 is moved to a location opposing the magnetic sensor 4.
The measured surface 6d of the subject 6 comes close to the
magnetic sensor 4. Next, the flow proceeds to step S6. Step S6 is a
measurement step. In this step, the magnetic sensor control unit 70
causes the magnetic sensor driving device 55 to drive the magnetic
sensor 4. The magnetic sensor 4 detects a magnetic field coming out
of the chest 6c of the subject 6. Next, the flow proceeds to step
S7. Step S7 is a subject demounting step. In this step, the table 3
is moved out of the electromagnetic shield device 2, and the
subject 6 leaves the tilting table 18. Through the above steps, the
process of measuring a magnetic field of the subject 6 is
finished.
[0190] Next, with reference to FIGS. 9A to 12C, the magnetic field
measurement method will be described in more detail so as to
correspond to the steps illustrated in FIG. 8. FIGS. 9A to 12C are
schematic diagrams for explaining the magnetic field measurement
method. FIG. 9A is a diagram corresponding to the subject mounting
step of step S1. As illustrated in FIG. 9A, in step S1, the subject
6 is mounted on the tilting table 18. A half or more of the tilting
table 18 protrudes out of the electromagnetic shield device 2. The
Z-direction table 11 is located at a low position, and thus the
subject 6 easily moves onto the tilting table 18.
[0191] FIGS. 9A and 9B are diagrams corresponding to the
positioning step of step S2. As illustrated in FIG. 9A, in step S2,
the operator operates the input device 23 so as to input an
instruction for starting positioning. The laser pointer control
unit 71 outputs an instruction signal for applying the laser light
5c, to the shape sensor driving device 53. The shape sensor driving
device 53 receives the instruction signal so as to drive the laser
scanning unit 5a. The laser scanning unit 5a performs irradiation
with the laser light 5c in the -Z direction. The laser light 5c is
applied to a single point located in the -Z direction from the
laser scanning unit 5a.
[0192] As illustrated in FIG. 9B, the xiphisternum 6e is present on
the -Y direction side of the chest 6c in the subject 6. The
xiphisternum 6e is a protrusion which protrudes at the lower end of
sternum, and is present at a part called the pit of the stomach at
which the rib bows join together. Referring to FIG. 9A again, the
operator operates the input device 23 so as to input an instruction
for moving the X-direction table 13 in the X direction. The table
movement control unit 68 outputs a signal for moving the
X-direction table 13, to the table driving device 54. The table
driving device 54 drives the motor movement portion 17 to move the
X-direction table motor 16 in the +X direction. Consequently, the
grooved cylinder 15a is connected to the grooved rod 15b.
[0193] Next, the table driving device 54 drives the X-direction
table motor 16 to move the X-direction table 13 in the X direction.
The X-direction table 13 is moved in tracking of an instruction
which is input by the operator via the input device 23. The
operator causes the Y direction side of the xiphisternum 6e to be
irradiated with the laser light 5c.
[0194] Successively, the operator operates the input device 23 so
as to input an instruction for moving the Y-direction table 9. The
table movement control unit 68 outputs a signal for moving the
Y-direction table 9, to the table driving device 54. The table
driving device 54 drives the motor movement portion 17 to move the
X-direction table motor 16 in the -X direction. Consequently, the
grooved cylinder 15a is separated from the grooved rod 15b.
[0195] Next, the table driving device 54 drives the motor 10a to
move the Y-direction table 9 in the Y direction. The Y-direction
table 9 is moved in tracking of an instruction which is input by
the operator via the input device 23. The operator causes the
xiphisternum 6e to be irradiated with the laser light 5c.
Thereafter, the operator operates the input device 23 so as to
input information indicating that positioning of the subject 6 has
been finished.
[0196] A reference point 4b for checking a measurement point is set
in the magnetic sensor 4. A position of the reference point 4b in
the X direction is the same as the position in the X direction
where the laser light 5c is applied in step S2. A distance in the Y
direction between the position of the reference point 4b and a
position through which the laser light 5c passes is set to a
predetermined reference distance 4c.
[0197] FIG. 9C is a diagram corresponding to the measured surface
measurement step of step S3. In step S3, the operator causes the
subject 6 to take a normal breath. The subject 6 may take a deep
breath so as to control his or her breathing. The operator operates
the input device 23 so as to input an instruction for starting
measurement of a stereoscopic shape of the measured surface 6d. The
shape measurement control unit 66 receives the instruction for
starting measurement, and outputs an instruction signal for
applying the laser light 5c, to the shape sensor driving device 53.
As illustrated in FIG. 9C, the laser scanning unit 5a irradiates
the measured surface 6d with the laser light 5c, and reciprocally
moves the reflection point 5d in the X direction. The imaging
device 5b receives the reflected light 5f. Since the reflection
point 5d is reciprocally moved on the measured surface 6d, the
imaging device 5b captures an image in which the reflection point
5d forms a line. The measured surface 6d is uneven, and the image
is an image of a curve. The shape sensor driving device 53
calculates a distance from the laser scanning unit 5a to the
reflection point 5d by using the image data and a triangulation
method, and outputs the calculated distance to the memory 52. The
memory 52 stores data regarding the distance from the laser
scanning unit 5a to the reflection point 5d as a part of the
measurement portion shape data 61.
[0198] The shape measurement control unit 66 outputs an instruction
signal for moving the Y-direction table 9 to the table driving
device 54 in cooperation with the table movement control unit 68. A
movement range of the Y-direction table 9 is the same as a range of
the measured surface 6d. The table driving device 54 moves the
Y-direction table 9 in the -Y direction and then moves the
Y-direction table 9 in the +Y direction at a predetermined speed.
The table driving device 54 outputs data indicating a position of
the Y-direction table 9 in the Y direction to the memory 52.
Consequently, the measurement portion shape data 61 of the memory
52 accumulates data regarding the distance between the laser
scanning unit 5a and the reflection point 5d on the measured
surface 6d. Next, the shape measurement control unit 66 subtracts a
value of the distance between the shape measurement device 5 and
the opposing surface 4e from the measurement portion shape data 61.
Consequently the measurement portion shape data 61 becomes data
regarding a distance 61a between the opposing surface 4e and the
chest 6c.
[0199] When the shape measurement device 5 completes the
measurement within the range of the measured surface 6d, the table
movement control unit 68 outputs an instruction signal for moving
the Y-direction table 9 to the table driving device 54 so that the
xiphisternum 6e is located at the location opposing the laser
scanning unit 5a. The table driving device 54 receives the
instruction signal and moves the Y-direction table 9. The operator
gives a message that the subject 6 is allowed to take a deep
breath.
[0200] FIGS. 10A to 10C are diagrams corresponding to the average
plane calculation step of step S4. As illustrated in FIGS. 10A and
10B, in step S4, the average plane calculation unit 67 calculates
an average plane on the measured surface 6d. The measurement
portion shape data 61 is data regarding a combination of an X
coordinate and a Y coordinate of each measurement point, and the
distance 61a. A measured surface 72 in the FIGS. 10A to 10C
represents a shape obtained by plotting the measurement portion
shape data 61. A measurement range 72a indicates a range of the
measured surface 6d where a magnetic field is measured. The
measured surface 72 is uneven in the measurement range 72a. The
average plane calculation unit 67 calculates coefficients of an
equation representing an average plane 73 by using a least square
method and an approximation method. Specifically, in an equation of
aX+bY+cZ+d=0, the coefficients a, b, c and d are calculated.
[0201] FIG. 10C is a diagram illustrating that the average plane 73
is moved from the measured surface 72 in the Z direction. In FIG.
10C, the average plane 73 and a horizontal plane 74 are
illustrated. The horizontal plane 74 corresponds to an initial
state of the tilting table 18, and indicates an upper surface of
the tilting table 18 when tilting is not performed. The average
plane calculation unit 67 calculates a tilt direction 73a of the
average plane 73. The tilt direction 73a is a direction in which a
tilt angle is the maximum. An angle of the tilt direction 73a on
the horizontal plane 74 is referred to as a tilt direction azimuth
angle 73b. An angle formed between the average plane 73 and the
horizontal plane 74 in the tilt direction 73a is referred to as a
tilt direction deviation angle 73c. The average plane calculation
unit 67 calculates the tilt direction azimuth angle 73b and the
tilt direction deviation angle 73c by using the equation
representing the average plane 73.
[0202] Next, the average plane calculation unit 67 calculates an
X-direction component and a Y-direction component of the tilt
direction deviation angle 73c. Successively, an angle of the
Y-direction component of the tilt direction deviation angle 73c is
multiplied by a distance of a Y-direction component between the
first tilting portion 26a and the second tilting portion 26b.
Consequently, a difference between a distance by which the first
tilting portion 26a is moved up and a distance by which the second
tilting portion 26b is moved up is calculated. Next, an angle of
the X-direction component of the tilt direction deviation angle 73c
is multiplied by a distance of an X-direction component between the
second tilting portion 26b and the third tilting portion 26c.
Consequently, a difference between a distance by which the second
tilting portion 26b is moved up and a distance by which the third
tilting portion 26c is moved up is calculated. A rise distance of a
portion which is not required to be moved up is set to 0 among the
first tilting portion 26a to the third tilting portion 26c. Rise
distances of the first tilting portion 26a to the third tilting
portion 26c are calculated. The average plane calculation unit 67
calculates a location where the distance 61a between the opposing
surface 4e and the measured surface 6d is shortest when the average
plane 73 is set to be parallel to the horizontal plane 74, and the
distance 61a.
[0203] FIGS. 11A and 11B are diagrams corresponding to the table
movement step of step S5. As illustrated in FIG. 11A, the table
movement control unit 68 causes the table driving device 54 to tilt
the tilting table 18. First, the tilting table 18 is tilted with
the X direction as an axis. At this time, the table movement
control unit 68 expands the second tilting portion 26b and the
third tilting portion 26c by the same length, and expands the first
tilting portion 26a. The first tilting portion 26a to the third
tilting portion 26c are expanded so that a Y-direction component of
an inclination of the tilt direction 73a becomes horizontal.
[0204] Next, as illustrated in FIG. 11B, the table movement control
unit 68 tilts the tilting table 18 with the Y direction as an axis.
At this time, the table movement control unit 68 expands one of the
second tilting portion 26b and the third tilting portion 26c, and
contracts the other. An X-direction component of the tilt direction
deviation angle 73c is made horizontal. Consequently, the average
plane 73 can be made parallel to the horizontal plane 74.
[0205] FIG. 12A is a diagram corresponding to the table movement
step of step S5 and the measurement step of step S6. As illustrated
in FIG. 12A, in step S5, the table movement control unit 68 outputs
an instruction signal for moving the Y-direction table 9, to the
table driving device 54. The table driving device 54 receives the
instruction signal so as to move the Y-direction table 9 by the
reference distance 4c in the +Y direction. As a result, the
reference point 4b is located at a location opposing the
xiphisternum 6e, and the measured surface 6d is located at a
location opposing the magnetic sensor 4.
[0206] Next, the table movement control unit 68 outputs an
instruction signal for moving up the Z-direction table 11 to the
table driving device 54. The table driving device 54 receives the
instruction signal so as to move up the Z-direction table 11 in the
+Z direction. The Z-direction table 11 is moved up at the location
where the distance between the measured surface 6d and the opposing
surface 4e is shortest so that the distance becomes 5 mm. The
distance between the measured surface 6d and the opposing surface
4e is not limited to 5 mm, and may be changed depending on a body
shape of the subject 6. When the subject 6 takes a normal breath, a
state occurs in which the opposing surface 4e of the magnetic
sensor 4 is not in contact with the measured surface 6d. The
distance between the measured surface 6d and the opposing surface
4e is short within a range in which the subject 6 is not in contact
with the magnetic sensor 4. Since the magnetic sensor 4 vibrates
when the measured surface 6d is in contact with the magnetic sensor
4, the measurement accuracy is reduced. In the present embodiment,
since the subject 6 comes close to the magnetic sensor 4 within a
range in which the measured surface 6d is not in contact with the
magnetic sensor 4, the magnetic field measurement apparatus 1 can
detect a magnetic field of the measured surface 6d with high
accuracy.
[0207] If the magnetic sensor 4 becomes distant from the measured
surface 6d, the strength of a magnetic field detected by the
magnetic sensor 4 is in inverse proportion to the square of a
distance from the measured surface 6d. Therefore, detection
performance of the magnetic sensor 4 is reduced as the magnetic
sensor 4 becomes more distant from the measured surface 6d. In the
present embodiment, the measured surface 6d comes close to the
magnetic sensor 4 to the extent to which the measured surface 6d is
parallel to the opposing surface 4e, and is not in contact with the
magnetic sensor 4. Therefore, the magnetic field measurement
apparatus 1 can detect a magnetic field of the measured surface 6d
with high accuracy. The table 3 is moved, and the door 2d is
closed. Consequently, it is possible to prevent an external
magnetic field from entering the electromagnetic shield device 2
through the opening 2b.
[0208] FIGS. 12A to 12C are diagrams corresponding to the
measurement step of step S6. As illustrated in FIG. 12A, in step
S6, the magnetic sensor 4 detects the magnetic vector 50 which
travels in the first direction 4a from the measured surface 6d of
the subject 6. The magnetic sensor control unit 70 outputs an
instruction signal for starting measurement to the magnetic sensor
driving device 55. The magnetic sensor driving device 55 receives
the instruction signal for starting measurement, and drives the
laser light source 30 and the heater 49. The laser light source 30
applies the laser light 31. If light emission of the laser light
source 30 is stabilized, and the magnetic sensor 4 is stabilized at
a predetermined temperature, the measurement is started. The
strength of a magnetic field detected by the magnetic sensor 4 is
output as an electric signal. The magnetic sensor driving device 55
converts electric signals output from the first photodetector 47
and the second photodetector 48 into electric signals indicating
the strength of the magnetic field. The magnetic sensor driving
device 55 converts the electric signals indicating the strength of
the magnetic field into digital data which is then transmitted to
the memory 52 as the magnetic measurement data 65.
[0209] In FIG. 12B, a first region 75a to a sixteenth region 75r
indicate regions where the respective sensor elements 4d detect the
magnetic vector 50. The first region 75a to the sixteenth region
75r are disposed in a lattice form of four rows and four columns.
The xiphisternum 6e is disposed in the second region 75b. In this
arrangement, the magnetic sensor 4 can detect the magnetic vector
50 generated from the heart of the subject 6 without leakage within
the range of the first region 75a to the sixteenth region 75r.
[0210] FIG. 12C illustrates an example of change data of a magnetic
field detected by the magnetic sensor 4. A longitudinal axis
expresses the magnetic field strength, and the strength of an upper
part in FIG. 12C is higher than the strength of a lower part
therein. A transverse axis expresses a change in time, and time
changes from a left part to a right part in FIG. 12C. The strength
of the magnetic vector 50 detected by the sensor element 4d is
referred to as the magnetic field strength. A first change line 76a
indicates a change in the magnetic field strength in the twelfth
region 75m, and indicates a change in the magnetic field strength
on the upper left side of the heart. The upper left side of the
heart represents a position in the X direction and the Y direction.
A second change line 76b indicates a change in the magnetic field
strength in the fourth region 75d, and indicates a change in the
magnetic field strength on the lower left side of the heart. A
third change line 76c indicates a change in the magnetic field
strength in the second region 75b, and indicates a change in the
magnetic field strength on the lower right side of the heart. A
fourth change line 76d indicates a change in the magnetic field
strength in the tenth region 75j, and indicates a change in the
magnetic field strength on the upper right side of the heart.
Sixteen magnetic field strength change lines can be obtained from
the magnetic sensor 4. In FIG. 12C, for better viewing, four change
lines are illustrated.
[0211] The first change line 76a has a peak, and then the second
change line 76b has a peak. Next, the third change line 76c has a
peak, and then the fourth change line 76d has a peak. As mentioned
above, the peaks of the magnetic field strength move around the
heart. When the heart does not normally operate, waveforms of the
first change line 76a to the fourth change line 76d are deformed.
Therefore, the operator can diagnose heart diseases of the subject
6 by observing waveforms of the first change line 76a to the fourth
change line 76d.
[0212] After the measurement of a magnetic field is completed, the
Z-direction table 11 is moved down, and the Y-direction table 9 is
moved in the -Y direction, in the subject demounting step of step
S7. The subject 6 leaves the table 3, and thus the process of
measuring a magnetic field from the heart of the subject 6 is
finished.
[0213] As described above, according to the present embodiment, the
following effects are achieved.
[0214] (1) According to the present embodiment, the magnetic field
measurement apparatus 1 includes the table 3, and the subject 6 is
mounted on the table 3. The shape measurement device 5 measures a
surface shape of the measured surface 6d of the subject 6. Next,
the average plane calculation unit 67 calculates the average plane
73 of the surface shape of the subject 6. The measured surface 6d
of the subject 6 is a curved surface, and the average plane
calculation unit 67 sets the average plane 73 so that deviation
with the measured surface 6d is minimized. Next, the table movement
control unit 68 controls a tilt of the table 3 so that the opposing
surface 4e is parallel to the average plane 73. The magnetic sensor
4 detects a magnetic field coming out of the subject 6 in a state
in which the opposing surface 4e of the magnetic sensor 4 is
parallel to the average plane 73, and the distance between the
average plane 73 and the opposing surface 4e is short.
[0215] As the subject 6 and the opposing surface 4e become more
distant from each other, a magnetic field reaching the opposing
surface 4e becomes weaker, and thus a signal-to-noise ratio (S/N
ratio) of a signal output from the magnetic sensor 4 is lowered. If
the subject 6 is in contact with the opposing surface 4e, the
magnetic sensor 4 receives vibration from the subject 6, and noise
increases due to the vibration. In the present embodiment, the
table movement control unit 68 can control a tilt of the table 3 so
as to make the average plane 73 parallel to the opposing surface 4e
of the magnetic sensor 4, and can cause the subject 6 to
sufficiently come close to the opposing surface 4e in a range in
which there is no contact therebetween. As a result, the magnetic
sensor 4 can detect a magnetic field coming out of the subject 6
with high sensitivity.
[0216] (2) According to the present embodiment, the table movement
control unit 68 controls the table 3 so that the distance between
the opposing surface 4e and the subject 6 becomes a predetermined
distance. The predetermined distance is longer than a distance
which the subject 6 moves through a normal action of the subject 6
such as breathing. The predetermined distance is short within a
range in which the subject 6 is not in contact with the magnetic
sensor 4. The table movement control unit 68 controls the table 3
so that the distance between the subject 6 and the opposing surface
4e becomes a distance which does not cause contact therebetween due
to an action of the subject 6. As a result, the subject 6 can be
made to come close to the magnetic sensor 4 within a range in which
the subject 6 is not in contact therewith.
[0217] (3) According to the present embodiment, the magnetic field
measurement apparatus 1 includes the electromagnetic shield device
2. The electromagnetic shield device 2 attenuates an entering
magnetic field line. The magnetic sensor 4 is provided inside the
electromagnetic shield device 2 so as to measure a magnetic field.
The electromagnetic shield device 2 includes the opening 2b and
attenuates a magnetic field line coming through the opening 2b.
Consequently, the electromagnetic shield device 2 can perform
measurement with less noise. The shape measurement device 5 is
provided in the opening 2b through which the subject 6 comes in and
out. Since the subject 6 passes near the shape measurement device
5, the shape measurement device 5 can easily measure a shape of the
measured surface 6d of the subject 6.
[0218] (4) According to the present embodiment, the shape
measurement device 5 scans the subject 6 with a light beam. A
location irradiated with the laser light 5c is measured. A surface
shape of the subject 6 has an unevenness, and a position where the
laser light 5c is reflected differs on the unevenness. Therefore,
the shape measurement device 5 can easily detect a surface shape of
the subject 6 by detecting a position of the laser light 5c
reflected from the subject 6.
[0219] (5) According to the present embodiment, the shape
measurement device 5 has a function of a guide light irradiation
unit which applies the laser light 5c for guiding a position where
the subject 6 is mounted on the table 3, and a function of
measuring a shape of the subject 6. The xiphisternum 6e of the
subject 6 is positioned at a location indicated by the laser light
5c, and thus the subject 6 can be mounted at a predetermined
position on the table 3. The shape measurement device 5 also has a
function of measuring a shape of the subject 6 by irradiating the
subject 6 with a light beam. Therefore, it is possible to reduce
the number of constituent elements compared with a case where the
magnetic field measurement apparatus 1 separately includes the
guide light irradiation unit and the shape measurement device 5. As
a result, it is possible to manufacture the magnetic field
measurement apparatus 1 with high productivity.
[0220] (6) According to the present embodiment, the tilting table
18 is provided with the tilting devices 26 including the three
tilting portions. The table movement control unit 68 controls a
length of the tilting device 26 so as to tilt the subject 6.
Consequently, the average plane 73 of the subject 6 can be made
parallel to the opposing surface 4e. The table 3 may have a
structure in which a device controlling a tilt is provided at the
center thereof. In contrast to this structure, loads of the table 3
and the subject 6 can be distributed to three leg portions, and
thus it is possible to control a tilt of the table 3 with a
lightweight structure.
[0221] (7) According to the present embodiment, a portion of the
table 3 which is moved into the electromagnetic shield device 2 is
non-magnetic. Therefore, it is possible to prevent magnetization of
the table 3 from influencing measurement of a magnetic field.
[0222] (8) According to the present embodiment, a location where
the magnetic sensor 4 detects a magnetic field is a surface of the
chest 6c opposing the heart 6g. A magnetic field generated due to
the activity of the heart 6g is output from the surface of the
chest 6c. As a result, the magnetic sensor 4 can detect the
activity of the heart 6g.
[0223] (9) According to the present embodiment, the subject 6 is
mounted on the table 3, and a shape of the subject 6 is measured.
The average plane 73 of the subject 6 is calculated. The measured
surface 6d of the subject 6 is a curved surface, and the average
plane 73 is set so that deviation with the measured surface 6d is
minimized. Next, the table movement control unit 68 controls a tilt
of the table 3 so that the opposing surface 4e of the magnetic
sensor 4 is parallel to the average plane 73 of the subject 6. The
subject 6 is made to come close to the opposing surface 4e of the
magnetic sensor 4, and the magnetic sensor 4 detects the magnetic
vector 50 coming out of the subject 6. In the present embodiment,
the average plane 73 of the subject 6 is calculated. The table
movement control unit 68 controls a tilt of the table 3 so that the
average plane 73 is parallel to the opposing surface 4e of the
magnetic sensor 4. The subject 6 is made to come close to the
opposing surface 4e in a form in which the subject 6 hardly
contacts the opposing surface 4e. As a result, the magnetic sensor
4 can detect the magnetic vector 50 coming out of the subject 6
with high sensitivity.
Second Embodiment
[0224] In the present embodiment, with reference to the drawings, a
description will be made of characteristic examples of a living
body magnetic field measurement apparatus and a living body
magnetic field measurement method of measuring a heart magnetic
field generated from the heart by using the magnetic field
measurement apparatus. A difference between the present embodiment
and the first embodiment is that a shape of a table is deformed
according to a shape of a back of a subject. A description of the
same content as that in the first embodiment will not be
repeated.
[0225] With reference to FIGS. 13 to 18, a description will be made
of a structure of a living body magnetic field measurement
apparatus according to the present embodiment. FIG. 13 is a
schematic perspective view illustrating a configuration of the
living body magnetic field measurement apparatus. As illustrated in
FIG. 13, a living body magnetic field measurement apparatus 101
includes a contour measurement section 102 and a magnetic field
measurement section 103 as a measurement unit, and a controller 104
controlling the contour measurement section 102 and the magnetic
field measurement section 103.
[0226] The contour measurement section 102 includes a first
foundation 105, and a first rail 106 and a second rail 107 are
provided to be erect on the first foundation 105. A thickness
direction of the first foundation 105 is set to a Z direction. The
Z direction is a vertical direction. Directions in which an upper
surface of the first foundation 105 extends are set to an X
direction and a Y direction. The X direction and the Y direction
are a horizontal direction, and the X direction and the Y direction
are orthogonal to each other. The first rail 106 and the second
rail 107 are provided side by side in the X direction. A beam
portion 108 which crosslinks the first rail 106 with the second
rail 107 is provided at ends on the Z direction sides of the first
rail 106 and the second rail 107. The beam portion 108 can increase
the strength of the first rail 106 and the second rail 107.
[0227] A subject 109 is disposed at an intermediate location
between the first rail 106 and the second rail 107. The subject 109
stands on the first foundation 105 and faces the first rail 106.
The contour measurement section 102 is a device which measures a
surface shape or a contour of the subject 109. The first rail 106
is provided with a front stage 110, and the front stage 110 is
movable in a lifting manner along the first rail 106. A first motor
111 is provided at the first rail 106 on the first foundation 105
side, and a first linear movement mechanism 112 is provided inside
the first rail 106. The front stage 110 is lifted by the first
motor 111 and the first linear movement mechanism 112. The first
motor 111 is a stepping motor. The first linear movement mechanism
112 may employ a configuration in which a ball screw or a timing
belt and a pulley are combined with each other. In the present
embodiment, for example, the ball screw is used in the first linear
movement mechanism 112. The front stage 110 is provided with a
front sensor 113, and the front sensor 113 measures a surface shape
of the chest of the subject 109.
[0228] Similarly, the second rail 107 is provided with a back stage
114, and the back stage 114 is movable in a lifting manner along
the second rail 107. A second motor 115 is provided at the second
rail 107 on the first foundation 105 side, and a second linear
movement mechanism 116 is provided inside the second rail 107. The
back stage 114 is lifted by the second motor 115 and the second
linear movement mechanism 116. The same motor as the first motor
111 is used as the second motor 115. The same linear movement
mechanism as the first linear movement mechanism 112 may be used as
the second linear movement mechanism 116. A back sensor 117 is
provided in the back stage 114, and the back sensor 117 measures a
surface shape of a back of the subject 109 or the like.
[0229] The magnetic field measurement section 103 mainly includes
an electromagnetic shield device 118 as a magnetic shield unit, a
table 121, and a magnetic sensor 122 as a magnetic detection unit.
The electromagnetic shield device 118 includes a rectangular
tubular main body 118a so as to prevent a situation in which an
external magnetic field such as terrestrial magnetism enters a
space where the magnetic sensor 122 is disposed. In other words,
the influence of the external magnetic field on the magnetic sensor
122 is minimized by the electromagnetic shield device 118, and a
magnetic field in the location where the magnetic sensor 122 is
present is considerably lower than the external magnetic field. The
main body 118a extends in the Y direction, and thus functions as a
passive magnetic shield. The inside of the main body 118a is
hollow, and a sectional shape of surfaces (orthogonal planes in the
Y direction in the XZ section) passing through the X direction and
the Z direction is a substantially quadrangle shape. A sectional
shape of the main body 118a is a square shape. The electromagnetic
shield device 118 is provided with a first opening 118b on the -Y
direction side, and the table 121 protrudes out of the first
opening 118b. Regarding the size of the electromagnetic shield
device 118, for example, a length thereof in the Y direction is
about 200 cm, and one side of the first opening 118b is about 90
cm. The subject 109 laid down on the table 121 can come in and out
of the electromagnetic shield device 118 via the first opening 118b
along with the table 121.
[0230] The controller 104 is provided at a location separated from
the first opening 118b. The controller 104 makes an electric signal
flow so as to control the living body magnetic field measurement
apparatus 101. A magnetic field or a residual magnetic field is
generated due to the electric signal, and becomes noise when
detected by the magnetic sensor 122. Since the controller 104 is
present at the location separated from the first opening 118b, the
magnetic field or the residual magnetic field generated from the
controller 104 hardly reaches the magnetic sensor 122. As a result,
the magnetic sensor 122 can perform measurement with less
noise.
[0231] The main body 118a is made of a ferromagnetic material
having relative permeability of, for example, several thousands or
more, or a conductor having high conductivity. As the ferromagnetic
material, permalloy, ferrite, iron, chromium, cobalt-based
amorphous metal, or the like may be used. As the conductor having
high conductivity, for example, aluminum which has a magnetic field
reduction function due to an eddy current effect may be used. The
main body 118a may be formed by alternately stacking a
ferromagnetic material and a conductor having high conductivity. In
the present embodiment, for example, the main body 118a is formed
by alternately staking an aluminum plate and a permalloy plate as
two layers whose entire thickness is about 20 mm to 30 mm.
[0232] First correction coils (first Helmholtz coils 118c) as a
magnetic shield unit are provided at ends on the +Y direction side
and the -Y direction side of the main body 118a. The first
Helmholtz coils 118c are coils for correcting an entering magnetic
field which enters the internal space of the main body 118a. The
entering magnetic field indicates an external magnetic field which
passes through the first opening 118b and enters the internal
space. The entering magnetic field is strongest with respect to the
first opening 118b in the Y direction. The first Helmholtz coils
118c generate a magnetic field which cancels out the entering
magnetic field by using a current supplied from the controller
104.
[0233] The table 121 includes a second foundation 123. The second
foundation 123 is disposed on the bottom inside the main body 118a,
and extends from the inside of the main body 118a to the outside of
the first opening 118b through the first opening 118b in the Y
direction (a movable direction of the subject 109). A pair of
Y-direction rails 124 extending in the Y direction is provided on
the second foundation 123. A Y-direction table 125 which is moved
in the Y direction along the Y-direction rails 124 is provided on
the Y-direction rails 124. A Y-direction linear motion mechanism
126 which moves the Y-direction table 125 is provided between the
two Y-direction rails 124. The Y-direction linear motion mechanism
126 is coupled to the controller 104, and is operated in response
to an instruction from the controller 104.
[0234] A Z-direction table 127 is provided on the Y-direction table
125, and a lifting device (not illustrated) is provided between the
Y-direction table 125 and the Z-direction table 127. The lifting
device lifts the Z-direction table 127. Four X-direction rails 128
extending in the X direction are provided on a surface on the +Z
direction side of the Z-direction table 127. An X-direction table
129 which is moved in the X direction along the X-direction rails
128 is provided on the X-direction rails 128.
[0235] An X-direction linear movement mechanism 130 which moves the
X-direction table 129 in the X direction is provided on the -Y
direction side on the Z-direction table 127. The X-direction linear
movement mechanism 130 includes a pair of bearing portions 130a,
and the bearing portions 130a are provided to be erect on the
Z-direction table 127. The X-direction table 129 is located between
the two bearing portions 130a. The two bearing portions 130a
rotatably support a first screw rod 130b. A first penetration hole
(not illustrated) which penetrates in the X direction is provided
in the X-direction table 129, and the first screw rod 130b is
provided to penetrate through the first penetration hole of the
X-direction table 129. A female screw (not illustrated) is formed
on the first penetration hole, and the first screw rod 130b is
engaged with the female screw. A first handle 130c is provided at
one end on the -X direction side of the first screw rod 130b, and
the first handle 130c is fixed to the first screw rod 130b. If the
first handle 130c is rotated, the first screw rod 130b is rotated.
Since the first screw rod 130b is engaged with the female screw of
the X-direction table 129, if the first screw rod 130b is rotated,
the X-direction table 129 is moved in the X direction. Therefore,
an operator rotates the first handle 130c so as to move the
X-direction table 129 in the X direction.
[0236] A second handle 131 is provided on a side surface of the
X-direction table 129 directed in the -Y direction. The second
handle 131 is joined to a second screw rod 131a. A second
penetration hole (not illustrated) which intersects the first screw
rod 130b is provided in the X-direction table 129, and the second
screw rod 131a is inserted into the second penetration hole. A
female screw is formed on the second penetration hole, and the
second screw rod 131a is engaged with the female screw of the
second penetration hole. When the operator rotates the second
handle 131, the second screw rod 131a presses the first screw rod
130b so as to minimize of rotation of the first screw rod 130b.
Therefore, it is possible to prevent the X-direction table 129 from
being moved in the X direction by operating the second handle 131.
The second foundation 123, the Y-direction rails 124, the
Y-direction table 125, the Y-direction linear motion mechanism 126,
the Z-direction table 127, the X-direction rails 128, the
X-direction table 129, and the like constituting the table 121 are
made of non-magnetic materials such as a wood, a resin, a ceramic,
and non-magnetic metal.
[0237] In the electromagnetic shield device 118, a laser pointer
132 is provided on the +Z direction side of the first opening 118b.
The laser pointer 132 emits laser light 132a in the -Z direction.
The subject 109 is mounted to face upward on the table 121. The
chest of the subject 109 is irradiated with the laser light 132a.
The operator drives the Y-direction linear motion mechanism 126 to
move the Y-direction table 125 in the Y direction. The operator
operates the first handle 130c so as to move the X-direction table
129 in the X direction. Positions of the table 121 in the X
direction and the Y direction may be adjusted so that xiphisternum
109e of the subject 109 is irradiated with the laser light
132a.
[0238] The magnetic sensor 122 is provided inside the magnetic
field measurement section 103. The magnetic sensor 122 is a sensor
which detects a magnetic field generated from the heart of the
subject 109. The magnetic sensor 122 is fixed to the
electromagnetic shield device 118. The location where the magnetic
field measurement section 103 is disposed is adjusted to a state in
which no magnetic field is substantially present by the
electromagnetic shield device 118. Therefore, the magnetic sensor
122 can measure a magnetic field generated from the heart without
being influenced by noise. The magnetic sensor 122 detects an
intensity component of a magnetic field in a first direction 122a
which is the same direction as the Z direction.
[0239] The controller 104 is provided with a display device 133 and
an input device 134. The display device 133 is a liquid crystal
display (LCD) or an organic light emitting diode (OLED). A
measurement situation, a measurement result, and the like are
displayed on the display device 133. The input device 134 is
constituted of a keyboard, a rotary knob, or the like. An operator
operates the input device 134 so as to input various instructions
such as a measurement starting instruction or a measurement
condition to the living body magnetic field measurement apparatus
101.
[0240] FIG. 14A is a schematic side view illustrating a structure
of the contour measurement section, and FIG. 14B is a schematic top
view illustrating a structure of the contour measurement section
102. In FIGS. 14A and 14B, the front sensor 113 includes a laser
scanning unit 113a and an imaging device 113b. The laser scanning
unit 113a is built into the front sensor 113, and emits laser light
113c in the X direction. The laser scanning unit 113a performs
scanning with the laser light 113c in the Y direction. A front face
109a of the subject 109 is irradiated with the laser light 113c.
The laser light 113c is reflected from the front face 109a. A
reflection point 113d at which the laser light 113c is reflected
from the front face 109a is linear when viewed from the front
sensor 113.
[0241] The imaging device 113b is provided at the front stage 110
via a support portion 110a. The imaging device 113b is provided to
be obliquely with respect to a traveling direction of the laser
light 113c. The imaging device 113b images reflected light 113e
which is reflected from the front face 109a of the subject 109. In
this case, the laser scanning unit 113a, the reflection point 113d,
and the imaging device 113b form a triangle. The distance between
the laser scanning unit 113a and the imaging device 113b is a known
value. An angle formed between the laser light 113c and the
reflected light 113e can be detected on the basis of an image
captured by the imaging device 113b. Therefore, the contour
measurement section 102 can measure the distance between the front
sensor 113 and the reflection point 113d by using a triangulation
method. As a result, it is possible to measure a first distance 135
which is the distance between the front sensor 113 and the front
face 109a of the subject 109.
[0242] The first motor 111 and the first linear movement mechanism
112 lift the front sensor 113. Consequently, the reflection point
113d is moved along the front face 109a of the subject 109. The
first distance 135 at each location of the front face 109a of the
subject 109 is measured. The first linear movement mechanism 112 is
provided with a length measurement device (not illustrated). A
position of the front stage 110 in the Z direction can be detected
by using the length measurement device. The length measurement
device includes a glass plate with a scale, and an optical sensor
detecting the scale. The optical sensor detects a position of the
glass plate. The laser light 113c is horizontally applied, and thus
a position of the reflection point 113d in the Z direction can be
detected. Since the laser light 113c is linearly applied to the
front face 109a, the contour measurement section 102 can measure a
stereoscopic shape of the front face 109a of the subject 109.
[0243] Similarly, the back sensor 117 includes a laser scanning
unit 117a and an imaging device 117b. The laser scanning unit 117a
is built into the back sensor 117, and emits laser light 117c in
the -X direction. The laser scanning unit 117a performs scanning
with the laser light 117c in the Y direction. The laser light 117c
is applied to a back face 109b as a second face of the subject 109.
The laser light 117c is reflected from the back face 109b. A
reflection point 117d where the laser light 117c is reflected from
the back face 109b is linear when viewed from the back sensor
117.
[0244] The imaging device 117b is provided at the back stage 114
via a support portion 114a. The imaging device 117b is provided to
be obliquely with respect to a traveling direction of the laser
light 117c. The imaging device 117b images reflected light 117e
which is reflected from the back face 109b of the subject 109. In
this case, the laser scanning unit 117a, the reflection point 117d,
and the imaging device 117b form a triangle. The distance between
the laser scanning unit 117a and the imaging device 117b is a known
value. An angle formed between the laser light 117c and the
reflected light 117e can be detected on the basis of an image
captured by the imaging device 117b. Therefore, the contour
measurement section 102 can measure the distance between the back
sensor 117 and the reflection point 117d by using a triangulation
method. As a result, it is possible to measure a second distance
136 which is the distance between the back sensor 117 and the back
face 109b of the subject 109.
[0245] The second motor 115 and the second linear movement
mechanism 116 lift the back sensor 117. Consequently, the
reflection point 117d is moved along the back face 109b of the
subject 109. The second distance 136 at each location of the back
face 109b of the subject 109 is measured. The second linear
movement mechanism 116 is provided with a length measurement device
(not illustrated). A position of the back stage 114 in the Z
direction can be detected by using the length measurement device.
The laser light 117c is horizontally applied, and thus a position
of the reflection point 117d in the Z direction can be detected.
Therefore, the contour measurement section 102 can measure a shape
of the back face 109b of the subject 109. Since a distance in the X
direction between the front sensor 113 and the back sensor 117 is
also a known value, it is possible to measure a subject width 137
which is the distance between the reflection point 113d and the
reflection point 117d by subtracting the first distance 135 and the
second distance 136 from the distance between the front sensor 113
and the back sensor 117.
[0246] FIGS. 15A and 15B are schematic sectional views illustrating
a structure of the table. FIG. 15A illustrates a state in which the
table 121 is being moved in the -Y direction, and FIG. 15B
illustrates a state in which the table 121 is moved into the
magnetic field measurement section 103, and a heart magnetic field
of the subject 109 is being measured. As illustrated in FIG. 15A,
the pair of first Helmholtz coils 118c is disposed on the second
foundation 123. A shape of the first Helmholtz coil 118c is a frame
shape, and is disposed to surround the main body 118a.
[0247] The Y-direction linear motion mechanism 126 includes a motor
126a. A first pulley 126b is provided on a rotation shaft of the
motor 126a, and a second pulley 126c is rotatably provided at an
end on the Y direction side of the Y-direction linear motion
mechanism 126. A timing belt 126d is hung on the first pulley 126b
and the second pulley 126c. A connection portion 126e is provided
on the timing belt 126d, and the connection portion 126e connects
the timing belt 126d to the Y-direction table 125. When the motor
126a rotates the first pulley 126b, the connection portion 126e is
moved in the Y direction by the torque of the motor 126a. The
Y-direction table 125 is moved due to the movement of the
connection portion 126e. Therefore, the motor 126a can move the
Y-direction table 125 in the Y direction. The motor 126a changes a
rotation direction of the first pulley 126b so as to move the
Y-direction table 125 in both directions such as the +Y direction
and the -Y direction.
[0248] Materials of the Y-direction rails 124, the second pulley
126c, the timing belt 126d, and the connection portion 126e are
non-magnetic materials. The timing belt 126d is made of rubber and
resin. The Y-direction rails 124, the second pulley 126c, and the
connection portion 126e are made of ceramics.
[0249] Four lifting devices 138 are provided side by side in the Y
direction in the Y-direction table 125. Each of the lifting devices
138 has a structure in which three air cylinders are arranged in
the X direction. The lifting device 138 expands and contracts the
air cylinders so as to lift the Z-direction table 127. Each air
cylinder is provided with a length measurement device (not
illustrated), and thus the lifting device 138 can detect a movement
amount of the Z-direction table 127. The respective air cylinders
move the Z-direction table 127 by the same distance, and thus the
lifting devices 138 can move the Z-direction table 127 in parallel.
Pneumatic equipment such as a compressor and an electromagnetic
valve (not illustrated) is provided in the controller 104. The
lifting devices 138 are controlled by the controller 104.
[0250] The X-direction table 129 is provided with wheels 140 which
are in contact with the X-direction rails 128. The wheels 140 are
rotated, and thus the X-direction table 129 can be easily moved in
the X direction. The Z-direction table 127, the X-direction rails
128, and the wheels 140 are made of ceramics which are non-magnetic
materials.
[0251] The magnetic sensor 122 is provided on the ceiling of the
main body 118a via a support member 141. A position of the center
of the magnetic sensor 122 in the Z direction is the central
position between the ceiling of the main body 118a and the bottom
of the main body 118a. A position of the center of the magnetic
sensor 122 in the X direction is the central position between a
wall on the +X direction side of the main body 118a and a wall on
the -X direction side thereof. The distance between the center of
the magnetic sensor 122 in the Y direction and an end on the -Y
direction side of the main body 118a is twice longer than the
distance between the center of the magnetic sensor 122 and the wall
on the +Y direction side of the main body 118a. If the center of
the magnetic sensor 122 is located at this location, it is possible
for the magnetic sensor 122 to be hardly influenced by a magnetic
field which enters the electromagnetic shield device 118 from the
outside thereof.
[0252] Second correction coils (second Helmholtz coils 139) having
a cube frame shape are provided inside the electromagnetic shield
device 118. Specifically, at least three correction coils are
provided so as to be orthogonal to each other in the X direction,
the Y direction, and the Z direction. In the second Helmholtz coil
139 orthogonal to the X direction, a measurement space in which the
subject 109 is disposed during measurement and the magnetic sensor
122 are interposed between a pair of coils from the X direction
(left/right direction). The second Helmholtz coil 139 orthogonal to
the X direction may generate a magnetic field in the X direction
and may cancel out an external magnetic field in the X direction so
that an X component of a magnetic field of the measurement space
and the space in which the magnetic sensor 122 is disposed is
reduced to the extent or less of not having an adverse effect on
measurement. In the second Helmholtz coil 139 orthogonal to the Y
direction, the measurement space and the magnetic sensor 122 are
interposed between two pairs of coils (that is, four coils) from
the Y direction (front/rear direction). The second Helmholtz coil
139 may orthogonal to the Y direction generate a magnetic field in
the Y direction and may cancel out an external magnetic field in
the Y direction so that a Y component of a magnetic field of the
measurement space and the space in which the magnetic sensor 122 is
disposed is reduced to the extent or less of not having an adverse
effect on measurement. Since the main body 118a has a tubular shape
extending in the front/rear direction, and an entering magnetic
field is considerable in the Y direction, two pairs of second
Helmholtz coils 139 are provided regarding the Y direction. In the
second Helmholtz coil 139 orthogonal to the Z direction, the
measurement space and the magnetic sensor 122 are interposed
between a pair of coils from the Z direction (upper/lower
direction). The second Helmholtz coil 139 orthogonal to the Z
direction may generate a magnetic field in the Z direction and may
cancel out an external magnetic field in the Z direction so that a
Z component of a magnetic field of the measurement space and the
space in which the magnetic sensor 122 is disposed is reduced to
the extent or less of not having an adverse effect on measurement.
The second Helmholtz coil 139 has a square frame shape when viewed
from each orthogonal direction side, and is disposed so that the
central position of the square frame overlaps the central position
of the magnetic sensor 122. A length of the side of the square is
not particularly limited, but, in the present embodiment, a length
of one side is equal to or more than 75 cm and equal to or less
than 85 cm. In FIGS. 15A and 15B, the shape of the second Helmholtz
coil 139 is a rectangular shape for better viewing, but is actually
a square shape.
[0253] Four second Helmholtz coils 139 having the square frame
shape are disposed at the same interval in the Y direction. When
viewed from the X direction, an outer circumference of the second
Helmholtz coil 139 has a square frame shape, and there is a
structure in which two coils are disposed inside the square frame
shape. The second Helmholtz coil 139 is disposed so that the
central position of the square frame shape overlaps the central
position of the magnetic sensor 122.
[0254] A shape of the second Helmholtz coil 139 viewed from the Z
direction is the same as the shape viewed from the X direction. The
second Helmholtz coil 139 is disposed so that the central position
of the square frame shape overlaps the central position of the
magnetic sensor 122.
[0255] The second Helmholtz coil 139 has such a shape, and thus it
is possible to further reduce a disturbance magnetic field in the
magnetic sensor 122. Particularly, it is possible to reduce the
influence of a magnetic flux which comes from the -Y direction side
of the electromagnetic shield device 118.
[0256] When the table 121 is located on the -Y direction side of
the electromagnetic shield device 118, a half or more of the table
121 protrudes out of the electromagnetic shield device 118.
Consequently, the subject 109 is easily mounted on the table 121.
When the subject 109 is mounted on the table 121, a height from the
floor to the nose of the subject 109 is smaller than a height from
the floor to the surface on the -Z direction side of the magnetic
sensor 122. Therefore, when the Y-direction table 125 is moved in
the Y direction, the subject 109 does not interfere with the
magnetic sensor 122.
[0257] As illustrated in FIG. 15B, the Y-direction table 125 is
moved in the +Y direction, and then the Z-direction table 127 is
moved up. At this time, the chest 109c of the subject 109 is
located at a location opposing the magnetic sensor 122, and comes
close to the magnetic sensor 122. The surface of the chest 109c is
a measured surface 109d as a first surface.
[0258] FIG. 16A is a side view illustrating a structure of the
X-direction table. The X-direction table 129 includes a main body
portion 129a, and the main body portion 129a is provided with a
recess 129b on a surface on the Z direction side thereof. A length
of the recess 129b in the X direction is the same as a width of the
X-direction table 129 in the X direction. The recess 129b is
located at a location opposing the head to the knee of the subject
109 mounted on the X-direction table 129. Ten lifting portions
including a first lifting portion 142 to a tenth lifting portion
151 are provided side by side in the Y direction in the recess
129b. Each lifting portion has a structure in which three air
cylinders are arranged in the X direction.
[0259] A first reception portion 152 to a tenth reception portion
163 are respectively provided on the +Z direction sides of the
first lifting portion 142 to the tenth lifting portion 151. Each of
the first reception portion 152 to the tenth reception portion 163
has a prism shape extending in the X direction. The first lifting
portion 142 expands and contracts the three air cylinders so as to
lift the first reception portion 152. Each air cylinder includes a
length measurement device (not illustrated), and the first lifting
portion 142 detects a movement amount of the first reception
portion 152. The respective air cylinders move the first reception
portion 152 by the same distance, and thus the first lifting
portion 142 moves the first reception portion 152 in parallel.
[0260] The second lifting portion 143 to the tenth lifting portion
151 have the same structure as that of the first lifting portion
142. The second lifting portion 143 to the tenth lifting portion
151 can respectively move the second reception portion 153 to the
tenth reception portion 163 in parallel. Pneumatic equipment such
as a compressor and an electromagnetic valve (not illustrated) is
provided in the controller 104. The controller 104 controls an
amount of air supplied to the first lifting portion 142 to the
tenth lifting portion 151, and thus controls each movement amount
of the first lifting portion 142 to the tenth lifting portion
151.
[0261] Surfaces on the +Z direction sides of the first reception
portion 152 to the tenth reception portion 163 are respectively a
first division surface 152a to a tenth division surface 163a as
division surfaces. The first division surface 152a to the tenth
division surface 163a are collectively referred to as a contact
surface 164. The contact surface 164 is a surface in contact with
the subject 109 at the back face 109b. A shape of the contact
surface 164 corresponds to a shape of the back face 109b.
[0262] The number of division surfaces constituting the contact
surface 164 is preferably equal to or larger than 10 and equal to
or smaller than 20, and more preferably fifteen. Since ten or more
division surfaces are in contact with and support the subject 109,
the subject 109 can be stably supported, and the measured surface
109d can be directed in the Z direction. The number of division
surfaces is equal to or smaller than 20. Therefore, the controller
104 can easily control positions of the division surfaces. For
better viewing, the number of division surfaces in FIG. 16A is
10.
[0263] A width 165 of each of the division surfaces constituting
the contact surface 164 is equal to or more than 5 cm and equal to
or less than 15 cm, and more preferably 10 cm. Since the division
surfaces are in contact with and support the subject 109 at the
interval of 5 cm to 15 cm, the subject 109 can be stably supported,
and the measured surface 109d can be directed in the Z
direction.
[0264] FIG. 16B is a main portion schematic enlarged view for
explaining a movable range of the division surface. In FIG. 16B,
the first lifting portion 142 is in a state of being expanded most.
The second lifting portion 143 is in a state of being contracted
most. In this case, a difference between the first division surface
152a and the second division surface 153a as a division surface is
a movable range 166. The movable range 166 is preferably equal to
or more than 3 cm and equal to or less than 10 cm. In this case,
the contact surface 164 can match the shape of the back face 109b
of the subject 109. Therefore, since the first division surface
152a to the tenth division surface 163a are in contact with and
support the subject 109, the subject 109 can be stably supported,
and the measured surface 109d can be directed in the +Z direction.
Since the movable range is equal to or less than 10 cm, the
controller 104 can easily control the division surfaces.
[0265] FIG. 16C is a top sectional view for explaining a
configuration of a tube, and is a view in which the magnetic field
measurement section 103 is cut on an XY plane crossing a support
member 141. FIG. 16D is a side sectional view for explaining a
configuration of the tube, and is a view in which the magnetic
field measurement section 103 is cut on a YZ plane along the wall
on the -Z direction side of the electromagnetic shield device
118.
[0266] The magnetic field measurement section 103 is provided with
a first tube 167 as a tube and a second tube 168 as a tube. A wire
through which electricity for driving the magnetic sensor 122 flows
is provided in the first tube 167. The second tube 168 includes a
tube through which air for driving the lifting devices 138 and the
first lifting portion 142 to the tenth lifting portion 151
flows.
[0267] A second opening 118d and a third opening 118e are provided
on a side surface of the -X direction side of the main body 118a.
The first tube 167 is disposed through the second opening 118d and
allows the inside and the outside of the electromagnetic shield
device 118 to communicate with each other. In the second opening
118d, the first tube 167 extends in a direction orthogonal to the
first direction 122a. In the second opening 118d, a direction of a
magnetic vector passing through the first tube 167 is orthogonal to
the first direction 122a. Therefore, the magnetic vector entering
the electromagnetic shield device 118 through the first tube 167
hardly influences the magnetic sensor 122.
[0268] Similarly, the second tube 168 is disposed through the third
opening 118e and causes the inside and the outside of the
electromagnetic shield device 118 to communicate with each other.
In the third opening 118e, the second tube 168 extends in a
direction orthogonal to the first direction 122a. In the third
opening 118e, a direction of a magnetic vector entering the
electromagnetic shield device 118 through the second tube 168 is
orthogonal to the first direction 122a. Therefore, the magnetic
vector entering the electromagnetic shield device 118 through the
second tube 168 hardly influences the magnetic sensor 122. As a
result, the magnetic field measurement section 103 can perform
measurement with less noise.
[0269] The direction in which the electromagnetic shield device 118
extends is set to a second direction 118f. The second direction
118f is a direction orthogonal to the first direction 122a. The
first tube 167 extends in the second direction 118f along the main
body 118a. Therefore, arrangement is obtained in which the first
tube 167 is easily provided. The first tube 167 extends in the
second direction 118f, and the second direction 118f is orthogonal
to the first direction 122a. Therefore, a magnetic vector passing
through the first tube 167 hardly influences the magnetic sensor
122. As a result, the magnetic field measurement section 103 can
perform measurement with less noise.
[0270] The second tube 168 has a structure of tending to be bent,
and the second tube 168 is bent twice at a bent portion 168a on the
-Y direction side. When the Y-direction table 125 is moved in the Y
direction, the bent portion 168a also is moved in the Y direction.
Consequently, the second tube 168 can be moved with high durability
without being twisted.
[0271] FIG. 17A is a schematic side view illustrating a structure
of the magnetic sensor, and FIG. 17B is a schematic plan view
illustrating a structure of the magnetic sensor. As illustrated in
FIGS. 17A and 17B, laser light 170 is supplied from a laser light
source 169 to the magnetic sensor 122. The laser light source 169
is provided in the controller 104, and the laser light 170 is
supplied to the magnetic sensor 122 through an optical fiber 171
provided in the first tube 167. The magnetic sensor 122 is coupled
to the optical fiber 171 via an optical connector 172.
[0272] The laser light source 169 outputs the laser light 170 with
a wavelength corresponding to an absorption line of cesium. A
wavelength of the laser light 170 is not particularly limited, but
is set to a wavelength of 894 nm corresponding to the D1-line, in
the present embodiment. The laser light source 169 is a tunable
laser device, and the laser light 170 output from the laser light
source 169 is continuous light with a predetermined light
amount.
[0273] The laser light 170 supplied via the optical connector 172
travels in the +X direction and is applied to a polarization plate
173. The laser light 170 having passed through the polarization
plate 173 is linearly polarized. The laser light 170 is
sequentially applied to a first half mirror 174, a second half
mirror 175, a third half mirror 176, and a first reflection mirror
177. Some of the laser light 170 is reflected by the first half
mirror 174, the second half mirror 175, and the third half mirror
176 so as to travel in the -Y direction. The other light is
transmitted therethrough so as to travel in the +X direction. The
first reflection mirror 177 reflects the entire incident laser
light 170 in the -Y direction. An optical path of the laser light
170 is divided into four optical paths by the first half mirror
174, the second half mirror 175, the third half mirror 176, and the
first reflection mirror 177. Reflectance of each mirror is set so
that light intensities of the laser light beams 170 on the
respective optical paths are the same as each other.
[0274] Next, the laser light 170 is sequentially applied to a
fourth half mirror 178, a fifth half mirror 181, a sixth half
mirror 182, and a second reflection mirror 183. Some of the laser
light 170 is reflected by the fourth half mirror 178, the fifth
half mirror 181, and the sixth half mirror 182 so as to travel in
the +Z direction. The other light 170 is transmitted therethrough
so as to travel in the -Y direction. The second reflection mirror
183 reflects the entire incident laser light 170 in the +Z
direction. A single optical path of the laser light 170 is divided
into four optical paths by the fourth half mirror 178, the fifth
half mirror 181, the sixth half mirror 182, and the second
reflection mirror 183. Reflectance of each mirror is set so that
light intensities of the laser light beams 170 on the respective
optical paths are the same as each other. Therefore, the optical
path of the laser light 170 is divided into the sixteen optical
paths. In addition, reflectance of each mirror is set so that light
intensities of the laser light beams 170 on the respective optical
paths are the same as each other.
[0275] Gas cells 184 are provided on the respective optical paths
of the laser light 170 on the +Z direction side of the fourth half
mirror 178, the fifth half mirror 181, the sixth half mirror 182,
and the second reflection mirror 183. The number of gas cells 184
is 16 in four rows and four columns. The laser light beams 170
reflected by the fourth half mirror 178, the fifth half mirror 181,
the sixth half mirror 182, and the second reflection mirror 183
pass through the gas cells 184. The gas cell 184 is a box having a
cavity therein, and an alkali metal gas is enclosed in the cavity.
The alkali metal is not particularly limited, and potassium,
rubidium, or cesium may be used. In the present embodiment, for
example, cesium is used as the alkali metal.
[0276] A polarization separator 185 is provided on the +Z direction
side of each gas cell 184. The polarization separator 185 is an
element which separates the incident laser light 170 into two
polarization components of the laser light 170, which are
orthogonal to each other. As the polarization separator 185, for
example, a Wollaston prism or a polarized beam splitter may be
used.
[0277] A first photodetector 186 is provided on the +Z direction
side of the polarization separator 185, and a second photodetector
187 is provided on the -Y direction side of the polarization
separator 185. The laser light 170 having passed through the
polarization separator 185 is applied to the first photodetector
186, and the laser light 170 reflected by the polarization
separator 185 is applied to the second photodetector 187. The first
photodetector 186 and the second photodetector 187 output currents
corresponding to an amount of incident laser light 170 to the
controller 104. If the first photodetector 186 and the second
photodetector 187 generate magnetic fields, this may influence
measurement, and thus it is preferable that the first photodetector
186 and the second photodetector 187 are made of a non-magnetic
material. The magnetic sensor 122 includes heaters 188 which are
provided on both sides in the X direction and both sides in the Y
direction. Each of the heaters 188 preferably has a structure in
which a magnetic field is not generated, and may employ, for
example, a heater of a type of performing heating by causing steam
or hot air to pass through a flow passage. Instead of using a
heater, the gas cell 184 may be inductively heated by using a high
frequency voltage.
[0278] The magnetic sensor 122 is disposed on the +Z direction side
of the subject 109. A magnetic vector 189 generated from the
subject 109 enters the magnetic sensor 122 from the -Z direction
side. The magnetic vector 189 passes through the fourth half mirror
178 to the second reflection mirror 183, and then passes through
the gas cell 184. The magnetic vector 189 passes through the
polarization separator 185, and comes out of the magnetic sensor
122.
[0279] The magnetic sensor 122 is a sensor which is called an
optical pumping type magnetic sensor or an optical pumping atom
magnetic sensor. Cesium in the gas cell 184 is heated and is
brought into a gaseous state. The cesium gas is irradiated with the
linearly polarized laser light 170, and thus cesium atoms are
excited so that orientations of magnetic moments can be aligned.
When the magnetic vector 189 passes through the gas cell 184 in
this state, the magnetic moments of the cesium atoms precess due to
a magnetic field of the magnetic vector 189. This precession is
referred to as Larmore precession. The magnitude of the Larmore
precession has a positive correlation with the strength of the
magnetic vector 189. In the Larmore precession, a polarization
plane of the laser light 170 is rotated. The magnitude of the
Larmore precession has a positive correlation with a change amount
of a rotation angle of the polarization plane of the laser light
170. Therefore, the strength of the magnetic vector 189 has a
positive correlation with the change amount of a rotation angel of
the polarization plane of the laser light 170. The sensitivity of
the magnetic sensor 122 is high in the first direction 122a in the
magnetic vector 189, and is low in the direction orthogonal to the
first direction 122a.
[0280] The polarization separator 185 separates the laser light 170
into two components of linearly polarized light which are
orthogonal to each other. The first photodetector 186 and the
second photodetector 187 respectively detect the strengths of the
two components of linearly polarized light orthogonal to each
other. Consequently, the first photodetector 186 and the second
photodetector 187 can detect a rotation angle of a polarization
plane of the laser light 170. The magnetic sensor 122 can detect
the strength of the magnetic vector 189 on the basis of a change of
the rotation angel of the polarization plane of the laser light
170. An element constituted of the gas cell 184, the polarization
separator 185, the first photodetector 186, and the second
photodetector 187 is referred to as a sensor element 122d. In the
present embodiment, sixteen sensor elements 122d of four rows and
four columns are disposed in the magnetic sensor 122. The number
and arrangement of the sensor elements 122d in the magnetic sensor
122 are not particularly limited. The sensor elements 122d may be
disposed in three or less rows or five or more rows. Similarly, the
sensor elements 122d may be disposed in three or less columns or
five or more columns. The larger the number of sensor elements
122d, the higher the spatial resolution.
[0281] FIG. 18 is an electrical control block diagram of the
controller. As illustrated in FIG. 18, the living body magnetic
field measurement apparatus 101 includes the controller 104
controlling an operation of the living body magnetic field
measurement apparatus 101. The controller 104 includes a central
processing unit (CPU) 190 which performs various calculation
processes as a processor, and a memory 191 which stores various
information. A sensor lifting driving device 192, a contour sensor
driving device 193, a table driving device 194, the laser pointer
132, the electromagnetic shield device 118, a magnetic sensor
driving device 195, the display device 133, and the input device
134 are coupled to the CPU 190 via an input/output interface 196
and a data bus 197.
[0282] The sensor lifting driving device 192 is a device driving
the front stage 110 and the back stage 114. The sensor lifting
driving device 192 receives an instruction signal for moving
positions of the front stage 110 and the back stage 114 from the
CPU 190. The front stage 110 and the back stage 114 respectively
include length measurement devices which detect positions thereof,
and the sensor lifting driving device 192 detects positions of the
front stage 110 and the back stage 114.
[0283] The sensor lifting driving device 192 calculates a
difference between a position to which the front stage 110 is
scheduled to be moved and the present position of the front stage
110. The sensor lifting driving device 192 drives the first motor
111 to move the front stage 110 to the position to which the first
motor 111 is scheduled to be moved. Similarly, the sensor lifting
driving device 192 calculates a difference between a position to
which the back stage 114 is scheduled to be moved and the present
position of the back stage 114. The sensor lifting driving device
192 drives the second motor 115 to move the back stage 114 to the
position to which the back stage 114 is scheduled to be moved.
[0284] The contour sensor driving device 193 is a device driving
the front sensor 113 and the back sensor 117. The contour sensor
driving device 193 drives the laser scanning unit 113a to emit the
laser light 113c toward the subject 109. The contour sensor driving
device 193 causes scanning to be performed with the laser light
113c in the horizontal direction. The contour sensor driving device
193 drives the imaging device 113b to capture an image of the
reflection point 113d. Similarly, the contour sensor driving device
193 drives the laser scanning unit 117a to emit the laser light
117c toward the subject 109. The contour sensor driving device 193
causes scanning to be performed with the laser light 117c in the
horizontal direction. The contour sensor driving device 193 drives
the imaging device 117b to capture an image of the reflection point
117d.
[0285] The table driving device 194 is a device driving the
Y-direction table 125, the Z-direction table 127, and the first
lifting portion 142 to the tenth lifting portion 151. The table
driving device 194 receives an instruction signal for moving a
position of the Y-direction table 125 from the CPU 190. The
Y-direction table 125 includes a length measurement device which
detects a position thereof, and the table driving device 194
detects a position of the Y-direction table 125. A difference
between a position to which the Y-direction table 125 is scheduled
to be moved and the present position of the Y-direction table 125
is calculated. The table driving device 194 drives the motor 126a
to move the Y-direction table 125 to the position to which the
Y-direction table 125 is scheduled to be moved. Consequently, the
table driving device 194 can move the Y-direction table 125 between
the position inside the electromagnetic shield device 118 and the
position outside the electromagnetic shield device 118.
[0286] Similarly, the table driving device 194 receives an
instruction signal for moving a position of the Z-direction table
127 from the CPU 190. Each of the lifting devices 138 lifting the
Z-direction table 127 includes a length measurement device
detecting position of the Z-direction table 127, and the table
driving device 194 detects a position of the Z-direction table 127.
A difference between a position to which the Z-direction table 127
is scheduled to be moved and the present position of the
Z-direction table 127 is calculated. The lifting device 138 is an
air cylinder, and the table driving device 194 is provided with
pneumatic equipment such as a compressor or an electromagnetic
valve driving the lifting device 138. The table driving device 194
controls an amount of air supplied to the lifting device 138 so as
to move the Z-direction table 127 to the position to which the
Z-direction table 127 is scheduled to be moved.
[0287] Similarly, the table driving device 194 receives an
instruction signal for moving positions of the first division
surface 152a to the tenth division surface 163a from the CPU 190.
The first lifting portion 142 to the tenth lifting portion 151
which lift the first division surface 152a to the tenth division
surface 163a respectively include length measurement devices
measuring positions of the first division surface 152a to the tenth
division surface 163a, and the table driving device 194 detects
positions of the first division surface 152a to the tenth division
surface 163a. A difference between a position to which each of the
first division surface 152a to the tenth division surface 163a is
scheduled to be moved and the present position of each surface is
calculated. The first lifting portion 142 to the tenth lifting
portion 151 are air cylinders, and the table driving device 194 is
provided with pneumatic equipment such as a compressor or an
electromagnetic valve driving the first lifting portion 142 to the
tenth lifting portion 151. The table driving device 194 controls an
amount of air supplied to the first lifting portion 142 to the
tenth lifting portion 151 so as to move the first division surface
152a to the tenth division surface 163a to the positions to which
the first division surface 152a to the tenth division surface 163a
are scheduled to be moved.
[0288] The laser pointer 132 includes a light source emitting the
laser light 132a. The laser pointer 132 receives an instruction
from the CPU 190, and turns on and off the laser light 132a.
[0289] The electromagnetic shield device 118 includes the first
Helmholtz coil 118c and a sensor detecting an internal magnetic
field. The electromagnetic shield device 118 reduces an internal
magnetic field of the main body 118a by driving the first Helmholtz
coil 118c in response to an instruction from the CPU 190.
[0290] The magnetic sensor driving device 195 is a device driving
the magnetic sensor 122 and the laser light source 169. The
magnetic sensor 122 is provided with the first photodetector 186,
the second photodetector 187, and the heater 188. The magnetic
sensor driving device 195 drives the first photodetector 186, the
second photodetector 187, and the heater 188. The magnetic sensor
driving device 195 converts electric signals output from the first
photodetector 186 and the second photodetector 187 into digital
signals which are then output to the CPU 190. The magnetic sensor
driving device 195 drives the heater 188 so that the magnetic
sensor 122 is maintained at a predetermined temperature. The
magnetic sensor driving device 195 drives the laser light source
169 to supply the laser light 170 to the magnetic sensor 122.
[0291] The display device 133 displays predetermined information in
response to an instruction from the CPU 190. The operator operates
the input device 134 on the basis of the display content and inputs
the instruction content. The instruction content is transmitted to
the CPU 190.
[0292] The memory 191 is a concept including a semiconductor memory
such as a RAM or a ROM, a hard disk, and an external storage device
such as a DVD-ROM. In terms of a function, a storage region for
storing program software 198 in which control procedures of an
operation of the living body magnetic field measurement apparatus
101 are described, or a storage region for storing subject contour
data 201 which is data obtained by measuring a contour of the
subject 109 is set. In addition, a storage region for storing table
shape data 202 which is data indicating a shape of the contact
surface 164 in the table 121 is set.
[0293] Further, a storing region for storing table position data
203 which is data indicating a position of the Y-direction table
125, the Z-direction table 127, and the X-direction table 129 is
set. Still further, a storage region for storing magnetic sensor
related data 204 which is data such as parameters used to drive the
magnetic sensor 122 is set in the memory 191. Furthermore, a
storage region for storing magnetic measurement data 205 which is
data measured by the magnetic sensor 122 is set in the memory 191.
Moreover, a storage region functioning as a work area for the CPU
190, a temporary file, or the like, and other various storage
regions are set.
[0294] The CPU 190 controls measurement of a magnetic field
generated from the heart of the subject 109 according to the
program software 198 stored in the memory 191. As a specific
function realizing unit, the CPU 190 includes a contour measurement
control unit 206 which is a measurement unit. The contour
measurement control unit 206 controls measurement of a contour of
the subject 109 by lifting the front sensor 113 and the back sensor
117. The CPU 190 includes a table shape calculation unit 207 as a
control unit. The table shape calculation unit 207 calculates a
shape of the contact surface 164 in accordance with a shape of the
subject 109. The CPU 190 includes a table shape control unit 208 as
a control unit. The table shape control unit 208 performs control
for forming a shape of the contact surface 164 of the X-direction
table 129 so that the shape becomes the same as a shape of the
contact surface 164 calculated by the table shape calculation unit
207.
[0295] The CPU 190 includes a table movement control unit 209. The
table movement control unit 209 controls movement and stoppage
positions of the Y-direction table 125, the Z-direction table 127,
and the X-direction table 129. The CPU 190 includes an
electromagnetic shield control unit 210. The electromagnetic shield
control unit 210 performs control for minimizing a magnetic field
around the magnetic sensor 122 by driving the electromagnetic
shield device 118.
[0296] The CPU 190 includes a magnetic sensor control unit 211. The
magnetic sensor control unit 211 performs control for causing the
magnetic sensor driving device 195 to drive the magnetic sensor 122
to detect the strength of the magnetic vector 189. The CPU 190
includes a laser pointer control unit 212. The laser pointer
control unit 212 performs control for driving the laser pointer 132
to turn on and off the laser light 132a.
[0297] In the present embodiment, the above-described respective
functions of the living body magnetic field measurement apparatus
101 are realized in the program software by using the CPU 190, but,
in a case where the above-described respective functions can be
realized by a stand-alone electronic circuit (hardware) without
using the CPU 190, such an electronic circuit may be used.
[0298] Next, a description will be made of a living body magnetic
field measurement method using the above-described living body
magnetic field measurement apparatus 101 with reference to FIGS.
14A and 14B and FIGS. 19 to 22B. FIG. 19 is a flowchart
illustrating a living body magnetic field measurement method. In
the flowchart illustrated in FIG. 19, step S11 corresponds to a
contour measurement step. In this step, the contour measurement
section 102 measures a contour of the subject 109. Next, the flow
proceeds to step S12. Step S12 is a table shape calculation step.
In this step, the table shape calculation unit 207 calculates a
shape of the contact surface 164 of the X-direction table 129.
Next, the flow proceeds to step S13.
[0299] Step S13 is a table forming step. In this step, the table
shape control unit 208 forms a shape of the contact surface 164 of
the X-direction table 129. Next, the flow proceeds to step S14.
Step S14 is a subject mounting step. In this step, the subject 109
is mounted on the contact surface 164 of the X-direction table 129.
Next, the flow proceeds to step S15. Step S15 is a table movement
step. In this step, the table movement control unit 209 moves the
table 121 so that the chest 109c of the subject 109 is moved to a
location opposing the magnetic sensor 122. Next, the flow proceeds
to step S16.
[0300] Step S16 is a measurement step. In this step, the magnetic
sensor control unit 211 causes the magnetic sensor driving device
195 to drive the magnetic sensor 122 to measure a magnetic field
coming out of the chest 109c of the subject 109. Through the above
steps, the process of measuring a magnetic field of the subject 109
is finished.
[0301] Next, with reference to FIGS. 14A and 14B, and FIG. 20A to
FIG. 22B, the magnetic field measurement method will be described
in more detail so as to correspond to the steps illustrated in FIG.
19. FIG. 20A to FIG. 22B are schematic diagrams for explaining the
living body magnetic field measurement method.
[0302] FIGS. 14A and 14B, and FIG. 20A are diagrams corresponding
to the contour measurement step of step S11. As illustrated in
FIGS. 14A and 14B, the subject 109 is mounted on the first
foundation 105. The subject 109 is in a standing attitude. The
operator operates the input device 134 so as to input a distance
from the first foundation 105 to the abdomen of the subject 109.
The operator operates the input device 134 so as to input a
distance from the first foundation 105 to the neck of the subject
109. The operator operates the input device 134 so as to input the
height of the subject 109.
[0303] The contour measurement control unit 206 outputs an
instruction signal to the sensor lifting driving device 192 so as
to move the front stage 110 and the back stage 114. First, the
contour measurement control unit 206 moves down the front stage 110
and the back stage 114 to the first foundation 105. The contour
measurement control unit 206 outputs an instruction signal to the
contour sensor driving device 193 so as to drive the back sensor
117. The back sensor 117 measures the second distance 136. The
contour measurement control unit 206 performs both movement of the
front stage 110 and the back stage 114 and measurement using the
back sensor 117. Consequently, the contour measurement section 102
measures a shape of the back face 109b.
[0304] When the front sensor 113 is moved to the location opposing
the abdomen of the subject 109, the contour measurement control
unit 206 outputs an instruction signal to the contour sensor
driving device 193 so as to drive the front sensor 113. The front
sensor 113 measures the first distance 135. The contour measurement
control unit 206 performs both movement of the front stage 110 and
the back stage 114 and measurement using the front sensor 113 and
the back sensor 117. Consequently, the contour measurement section
102 measures shapes of the front face 109a and the back face
109b.
[0305] When the front sensor 113 is moved to the location opposing
the neck of the subject 109, the contour measurement control unit
206 outputs an instruction signal to the contour sensor driving
device 193 so as to stop the driving of the front sensor 113.
Thereafter, the contour measurement control unit 206 performs both
movement of the front stage 110 and the back stage 114 and
measurement using the back sensor 117. Consequently, the contour
measurement section 102 measures a shape of the back face 109b.
[0306] When the front stage 110 and the back stage 114 arrive up to
the height of the subject 109, the contour measurement control unit
206 outputs an instruction signal to the sensor lifting driving
device 192 so as to stop the movement of the front stage 110 and
the back stage 114. The contour measurement control unit 206
outputs an instruction signal to the contour sensor driving device
193 so as to stop the driving of the back sensor 117.
[0307] The contour sensor driving device 193 stores the measured
data in the memory 191 as the subject contour data 201. As a
result, as illustrated in FIG. 20A, a contour line 213 is formed.
In FIG. 20A, the solid line portion is the contour line 213
indicated by the measured data. In FIG. 20A, the dotted line
portion is a portion corresponding to no data. In the contour line
213, a front face line 213a is a line corresponding to the chest
109c of the subject 109. The front face line 213a is a line from
the abdomen to the neck of the subject 109. The subject contour
data 201 is three-dimensional shape data indicating the surface of
the chest 109c. The front face line 213a is a line intersecting the
YZ plane passing through the center of the heart in the
three-dimensional shape data. In the contour line 213, a back face
line 213b is a diagram corresponding to the back face 109b of the
subject 109. The back face line 213b is a line from the heel to the
head of the subject 109.
[0308] FIGS. 20B and 20C are diagrams corresponding to the table
shape calculation step of step S12. As illustrated in FIG. 20B, in
step S12, a reference plane 214 is set. The reference plane 214 is
parallel to the surface on the -Z direction side of the magnetic
sensor 122, and corresponds to a virtual plane which is moved from
the surface on the -Z direction side of the magnetic sensor 122 by
5 mm in the -Z direction. A normal direction of the reference plane
214 is the first direction 122a. The table shape calculation unit
207 rotates the contour line 213 with the X direction as a rotation
axis. The contour line 213 is moved in the +Z direction or the -Z
direction so that the front face line 213a is in contact with the
reference plane 214. The front face line 213a is a line
corresponding to the measured surface 109d. Rotation and movement
of the graphic are calculated by using affine transform. The back
face line 213b when the front face line 213a is in contact with the
reference plane 214 is set to a subject back face line 215. The
subject back face line 215 is a line used as a reference of a shape
of the contact surface 164. In other words, the table shape
calculation unit 207 calculates a shape of the back face 109b when
the normal direction of the measured surface 109d is set to the
first direction 122a.
[0309] As illustrated in FIG. 20C, the contact surface 164 is
calculated so as to be in contact with the subject back face line
215. First, the subject back face line 215 is disposed on the
X-direction table 129 so that a portion of the subject back face
line 215 corresponding to the calf of the leg is in contact with an
upper surface 129c of the X-direction table 129. The upper surface
129c of the X-direction table 129 is a surface directed in the +Z
direction side. Next, the table shape calculation unit 207 sets a
position of the tenth reception portion 163 so that the tenth
division surface 163a is in contact with the subject back face line
215.
[0310] Successively, the table shape calculation unit 207 sets a
position of the ninth reception portion 162 so that the ninth
division surface 162a as a division surface is in contact with the
subject back face line 215. Next, the table shape calculation unit
207 sets respective positions of the eighth reception portion 161
to the first reception portion 152 so that the eighth division
surface 161a to the first division surface 152a are in contact with
the subject back face line 215. The set first division surface 152a
to tenth division surface 163a correspond to the contact surface
164. In this case, the surface in contact with the front face line
213a is a parallel surface which is separated from the surface on
the -Z direction side of the magnetic sensor 122 by 5 mm.
[0311] FIG. 20D is a diagram corresponding to the table forming
step of step S13. As illustrated in FIG. 20D, in step S13, the
table shape control unit 208 adjusts the heights of the first
lifting portion 142 to the tenth lifting portion 151. Positions of
the first reception portion 152 to the tenth reception portion 163
in the Z direction are set to the positions of the first reception
portion 152 to the tenth reception portion 163 set in step S12. As
a result, the contact surface 164 on the X-direction table 129 is
in contact with the subject back face line 215 at a plurality of
locations. In other words, in steps S11 to step S13, when the
normal direction of the measured surface 109d is the same as the
first direction 122a, the contour measurement control unit 206, the
table shape calculation unit 207, the table shape control unit 208
control a shape of the contact surface 164 to be a shape
corresponding to the shape of the back face 109b.
[0312] FIG. 20E is a diagram corresponding to the subject mounting
step of step S14. As illustrated in FIG. 20E, in step S14, the
subject 109 is mounted on the contact surface 164 of the table 121.
Since the contact surface 164 has the shape corresponding to the
shape of the back face 109b of the subject 109, the back face 109b
of the subject 109 is in contact with the contact surface 164. In
this case, the back face 109b of the subject 109 is in contact with
each of the first division surface 152a to the tenth division
surface 163a, and thus the subject 109 is stably mounted on the
table 121. The surface on the -Z direction side of the magnetic
sensor 122, the reference plane 214, and the surface of the chest
109c are parallel to each other. The surface on the -Z direction
side of the magnetic sensor 122 is separated from the reference
plane 214 by 5 mm. In this step, the Z-direction table 127 is
located at a low position, and thus the reference plane 214 is
separated from the surface of the chest 109c by a predetermined
reference height 216.
[0313] FIGS. 21A to 21C are diagrams corresponding to the table
movement step of step S15. As illustrated in FIG. 21A, in step S15,
the laser pointer 132 performs irradiation with the laser light
132a in the -Z direction. The operator operates the first handle
130c of the X-direction linear movement mechanism 130 to move the
X-direction table 129. The operator operates the input device 134
of the controller 104 so that the Y-direction linear motion
mechanism 126 is driven. The Y-direction linear motion mechanism
126 moves the Y-direction table 125 in the Y direction.
[0314] As illustrated in FIG. 21B, the xiphisternum 109e is present
on the -Y direction side of the chest 109c in the subject 109. The
xiphisternum 109e is a protrusion which protrudes at the lower end
of sternum, and is present at a part called the pit of the stomach
at which the rib bows join together. Referring to FIG. 21A again,
the operator moves the Y-direction table 125 and the X-direction
table 129 so as to move a position of the subject 109. The
xiphisternum 109e is irradiation with the laser light 132a.
Thereafter, the operator operates the input device 134 so as to
input information indicating that positioning of the subject 109
has been finished.
[0315] A reference point 122b for checking a measurement point is
set in the magnetic sensor 122. A position of the reference point
122b in the X direction is the same as the position in the X
direction through the laser light 132a passes. A distance in the Y
direction between the position of the reference point 122b and the
position through which the laser light 132a passes is set to a
predetermined reference distance 122c.
[0316] As illustrated in FIG. 21C, successively, the table movement
control unit 209 outputs an instruction signal for moving the
Y-direction table 125, to the table driving device 194. The table
driving device 194 receives the instruction signal, and moves the
Y-direction table 125 in the +Y direction by the reference distance
122c. Next, the table movement control unit 209 outputs an
instruction signal for moving the Z-direction table 127, to the
table driving device 194. The table driving device 194 receives the
instruction signal, and moves up the Z-direction table 127 in the
+Z direction by the reference height 216. Consequently, the
measured surface 109d matches the reference plane 214.
[0317] As a result, the reference point 122b is located at a
location opposing the xiphisternum 109e, and the measured surface
109d is located at a location opposing the magnetic sensor 122. The
distance between the surface on the -Z direction side of the
magnetic sensor 122 and the measured surface 109d is 5 mm. The
operator checks whether or not the surface on the -Z direction side
of the magnetic sensor 122 comes into contact with the measured
surface 109d when the subject 109 takes a deep breath. In a case
where the magnetic sensor 122 comes into contact with the subject
109, the operator moves down the Z-direction table 127. The
operator operates the input device 134 so as to give an instruction
to the table movement control unit 209. Consequently, the magnetic
sensor 122 is not in contact with the subject 109 even when the
subject 109 takes a deep breath.
[0318] FIGS. 22A and 22B are diagrams corresponding to the
measurement step of step S16. As illustrated in FIG. 22A, in step
S16, the magnetic sensor 122 detects the magnetic vector 189 which
travels in the Z direction from the measured surface 109d of the
subject 109. The magnetic sensor control unit 211 outputs an
instruction signal for starting measurement to the magnetic sensor
driving device 195. The magnetic sensor driving device 195 receives
the instruction signal for starting measurement, and causes the
laser light source 169 to apply the laser light 170. If light
emission of the laser light source 169 is stabilized, and the
magnetic sensor 122 is stabilized at a predetermined temperature,
the measurement is started. The strength of a magnetic field
detected by the magnetic sensor 122 is output as an electric
signal. The magnetic sensor driving device 195 converts the
electric signal indicating the strength of the magnetic field into
digital data which is then transmitted to the memory 191 as the
magnetic measurement data 205.
[0319] In FIG. 22A, a first region 217a to a sixteenth region 217r
indicate regions where the respective sensor elements 122d detect
the magnetic vector 189. The first region 217a to the sixteenth
region 217r are disposed in a lattice form of four rows and four
columns. The xiphisternum 109e is disposed in the second region
217b. In this arrangement, the magnetic sensor 122 can detect the
magnetic vector 189 generated from the heart of the subject 109
within the range of the first region 217a to the sixteenth region
217r.
[0320] FIG. 22B illustrates an example of change data of a magnetic
field detected by the magnetic sensor 122. A longitudinal axis
expresses the magnetic field strength, and the strength of an upper
part in FIG. 22B is higher than the strength of a lower part
therein. A transverse axis expresses a change in time, and time
changes from a left part to a right part in FIG. 22B. The strength
of the magnetic vector 189 detected by the sensor element 122d is
referred to as the magnetic field strength. A first change line
218a indicates a change in the magnetic field strength in the
twelfth region 217m, and indicates a change in the magnetic field
strength on the upper left side of the heart. The upper left side
of the heart represents a position in the X direction and the Y
direction. A second change line 218b indicates a change in the
magnetic field strength in the fourth region 217d, and indicates a
change in the magnetic field strength on the lower left side of the
heart. A third change line 218c indicates a change in the magnetic
field strength in the second region 217b, and indicates a change in
the magnetic field strength on the lower right side of the heart. A
fourth change line 218d indicates a change in the magnetic field
strength in the tenth region 217j, and indicates a change in the
magnetic field strength on the upper right side of the heart.
Sixteen magnetic field strength change lines can be obtained from
the magnetic sensor 122. In FIG. 22B, for better viewing, four
change lines are illustrated.
[0321] The first change line 218a has a peak, and then the second
change line 218b has a peak. Next, the third change line 218c has a
peak, and then the fourth change line 218d has a peak. As mentioned
above, the peaks of the magnetic field strength move around the
heart. When the heart does not normally operate, waveforms of the
first change line 218a to the fourth change line 218d are deformed.
Therefore, the operator can diagnose heart diseases of the subject
109 by observing waveforms of the first change line 218a to the
fourth change line 218d.
[0322] After the measurement of a magnetic field is completed, the
Z-direction table 127 is moved down, and the Y-direction table 125
is moved in the -Y direction. The subject 109 is demounted from the
table 121, and thus the process of measuring a magnetic field from
the heart of the subject 109 is finished.
[0323] As described above, according to the present embodiment, the
following effects are achieved.
[0324] (1) According to the present embodiment, the magnetic sensor
122 detects a distribution of a component in the first direction
122a of the magnetic vector 189 of the measured surface 109d of the
subject 109. The magnetic sensor 122 has high sensitivity for a
component of the magnetic vector 189 in the first direction 122a,
and has low sensitivity for a component thereof orthogonal to the
first direction 122a. The measured surface 109d of the subject 109
is directed toward the magnetic sensor 122. The back face 109b is
directed toward the table 121, and the back face 109b is in contact
with the contact surface 164 of the table 121. The contour
measurement section 102 measures shapes of the measured surface
109d and the back face 109b. The contact surface 164 of the table
can be controlled. The table shape calculation unit 207 and the
table shape control unit 208 control the contact surface 164 to
have a shape corresponding to the back face 109b, and set the
normal direction of the measured surface 109d of the subject 109 to
be the same as the first direction 122a.
[0325] Therefore, the normal direction of the measured surface 109d
of the subject 109 can be adjusted to a direction in which the
sensitivity of the magnetic sensor 122 is high. If the normal
direction of the measured surface 109d is inclined with respect to
the first direction 122a, there may be the occurrence of a location
where the distance between the measured surface 109d and the
magnetic sensor 122 is short and a location where the distance
therebetween is long. The weaker strength of the magnetic vector
189 is detected at the location where the distance between the
measured surface 109d and the magnetic sensor 122 is short than at
the location where the distance therebetween is long, and thus
detection accuracy is reduced. In the present embodiment, the
normal direction of the measured surface 109d is the same as the
first direction 122a in which the magnetic vector 189 is detected.
As a result, it is possible to detect a distribution of the
magnetic vector 189 of the subject 109 with high accuracy.
[0326] (2) According to the present embodiment, the contact surface
164 is divided into a plurality of division surfaces moved in the
first direction 122a. Positions of the plurality of division
surfaces in the first direction 122a match the subject 109, and
thus the contact surface 164 can be made to correspond to a shape
of the back face 109b. The number of the plurality of division
surfaces is equal to or larger than 10. Therefore, since the ten or
more division surfaces are in contact with and support the subject
109, the subject 109 can be stably supported, and the measured
surface 109d can be made to be directed in a predetermined
direction. The number of the plurality of division surfaces is
equal to or smaller than 20. Therefore, the table shape control
unit 208 can easily control positions of the division surfaces.
[0327] (3) According to the present embodiment, a width of each of
the first division surface 152a to the tenth division surface 163a
is equal to or more than 5 cm and equal to or less than 15 cm, and
more preferably 10 cm. Therefore, since the division surfaces are
in contact with and support the subject 109 at the interval of 5 cm
to 15 cm, the subject 109 can be stably supported, and the measured
surface 109d can be directed in the first direction 122a.
[0328] (4) According to the present embodiment, a movable range of
the first division surface 152a to the tenth division surface 163a
in the first direction 122a is equal to or more than 3 cm and equal
to or less than 10 cm. Therefore, the contact surface 164 can match
the shape of the back face 109b of the subject 109. Thus, since the
division surfaces are in contact with and support the subject 109,
the subject 109 can be stably supported, and the measured surface
109d can be directed in the first direction 122a. Since the movable
range is equal to or less than 10 cm, it is possible to easily
control the division surfaces.
[0329] (5) According to the present embodiment, the electromagnetic
shield device 118 attenuates an entering magnetic field line. The
magnetic sensor 122 and the table 121 are provided inside the
electromagnetic shield device 118. The electromagnetic shield
device 118 is provided with the first opening 118b, and the subject
109 can come in and out of the electromagnetic shield device 118
via the first opening 118b. The controller 104 is located at a
location separated from the first opening 118b.
[0330] The controller 104 makes an electric signal flow so as to
control the table 121. A magnetic field is generated due to the
electric signal, and becomes noise when detected by the magnetic
sensor 122. In the present embodiment, since the controller 104 is
present at the location separated from the first opening 118b, the
magnetic field generated from the controller 104 hardly reaches the
magnetic sensor 122. As a result, the magnetic sensor 122 can
perform measurement with less noise.
[0331] (6) According to the present embodiment, the electromagnetic
shield device 118 is provided with the first tube 167 and the
second tube 168, and the first tube 167 and the second tube 168
extend in a direction orthogonal to the first direction 122a and
allow the inside and the outside of the electromagnetic shield
device 118 to communicate with each other. Directions of magnetic
vectors passing through the first tube 167 and the second tube 168
are orthogonal to the first direction 122a. Therefore, magnetic
vectors passing through the first tube 167 and the second tube 168
hardly influence the magnetic sensor 122. As a result, the magnetic
sensor 122 can perform measurement with less noise.
[0332] (7) According to the present embodiment, the first tube 167
and the second tube 168 extend in the second direction 118f, and
the second direction 118f is orthogonal to the first direction
122a. Therefore, magnetic vectors passing through the first tube
167 and the second tube 168 hardly influence the magnetic sensor
122. As a result, the magnetic sensor 122 can perform measurement
with less noise. The first tube 167 and the second tube 168 are
provided along the electromagnetic shield device 118, and
arrangement is obtained in which the first tube 167 the second tube
168 are easily provided.
[0333] (8) According to the present embodiment, in the contour
measurement step of step S11, shapes of the measured surface 109d
and the back face 109b of the subject 109 are measured. In the
table shape calculation step of step S12, a shape of the back face
109b is calculated when a normal direction of the measured surface
109d is set to be the same as a direction of the first direction
component. In the table forming step of step S13, the contact
surface 164 of the table 121 is formed to correspond to the
calculated shape of the back face 109b. In the subject mounting
step of step S14, the subject 109 is mounted on the contact surface
164 of the table 121. The contact surface 164 has a shape
corresponding to the back face 109b of the subject 109, and the
subject 109 is mounted so that the back face 109b thereof is in
contact with the contact surface 164. Therefore, the measured
surface 109d of the subject 109 can be directed in the first
direction 122a.
Third Embodiment
[0334] In the present embodiment, a description will be made of
characteristic examples of a living body magnetic field measurement
method of measuring a heart magnetic field generated from the heart
by using a magnetic field measurement apparatus. A difference
between the present embodiment and the second embodiment is that
the table 121 is moved into the electromagnetic shield device 118,
and then the contact surface 164 is changed. A description of the
same content as that in the second embodiment will not be
repeated.
[0335] In the present embodiment, the same steps as the steps in
the second embodiment are performed. The same steps as the contour
measurement step of step S11 to the subject mounting step of step
S14 in the second embodiment are performed. In the table movement
step of step S15, first, the table movement control unit 209 moves
the Y-direction table 125. The Y-direction table 125 moves the
measured surface 109d to a location opposing the magnetic sensor
122.
[0336] Next, the table shape control unit 208 controls the first
lifting portion 142 to the tenth lifting portion 151 to deform the
contact surface 164 to a shape corresponding to the shape of the
back face line 213b. Successively, the table movement control unit
209 controls the lifting devices 138 so that the measured surface
109d comes close to the magnetic sensor 122. The table driving
device 194 receives an instruction signal so as to move up the
Z-direction table 127 by the reference height 216 in the +Z
direction. Consequently, the measured surface 109d matches the
reference plane 214.
[0337] In the measurement step of step S16, the same step as the
step in the second embodiment is performed. Also in the
above-described method, the normal direction of the measured
surface 109d is the same as the first direction 122a in which the
magnetic vector 189 is detected. As a result, it is possible to
detect a distribution of the magnetic vector 189 of the subject 109
with high accuracy.
Fourth Embodiment
[0338] In the present embodiment, with reference to the drawings, a
description will be made of characteristic examples of a living
body magnetic field measurement apparatus and a living body
magnetic field measurement method of measuring a heart magnetic
field generated from the heart by using the magnetic field
measurement apparatus. A difference between the present embodiment
and the first embodiment is that a most protruding portion of a
measured surface is detected and is made to come close to a
magnetic sensor. A description of the same content as that in the
first embodiment will not be repeated.
[0339] In the present embodiment, with reference to the drawings, a
description will be made of characteristic examples of a living
body magnetic field measurement apparatus and a living body
magnetic field measurement method of measuring a heart magnetic
field generated from the heart by using the magnetic field
measurement apparatus. With reference to FIGS. 23 to 30, a
description will be made of a structure of a living body magnetic
field measurement apparatus according to the present embodiment.
FIG. 23 is a schematic perspective view illustrating a
configuration of the magnetic field measurement apparatus. As
illustrated in FIG. 23, a living body magnetic field measurement
apparatus 301 mainly includes an electromagnetic shield device 302
as a magnetic shield unit, a table 303, a magnetic sensor 304 as a
magnetic detection unit, and a position measurement device 305 as a
position measurement unit and a guide light irradiation unit.
[0340] The electromagnetic shield device 302 includes a rectangular
tubular main body 302a. A longitudinal direction of the main body
302a is set to a Y direction. The gravity direction is set to a -Z
direction, and a direction orthogonal to the Y direction and the Z
direction is set to an X direction. The electromagnetic shield
device 302 prevents an external magnetic field such as terrestrial
magnetism from entering a space where the magnetic sensor 304 is
disposed. That is, the influence of the external magnetic field on
the magnetic sensor 304 is minimized by the electromagnetic shield
device 302, and a magnetic field in the location where the magnetic
sensor 304 is present is considerably lower than the external
magnetic field. The main body 302a extends in the Y direction, and
the main body 302a functions as a passive magnetic shield. The
inside of the main body 302a is hollow, and a sectional shape of
surfaces (orthogonal planes in the Y direction in the XZ section)
passing through the X direction and the Z direction is a
substantially quadrangle shape. In the present embodiment a
sectional shape of the main body 302a is a square shape. The
electromagnetic shield device 302 is provided with a first opening
302b on the -Y direction side, and the table 303 protrudes out of
the first opening 302b. The size of the electromagnetic shield
device 302 is not particularly limited, but, in the present
embodiment, for example, a length thereof in the Y direction is
about 200 cm, and one side of the first opening 302b is about 90
cm. A subject 306 mounted on the table 303 can come in and out of
the electromagnetic shield device 302 via the first opening 302b
along with the table 303.
[0341] The main body 302a is made of a ferromagnetic material
having relative permeability of, for example, several thousands or
more, or a conductor having high conductivity. As the ferromagnetic
material, permalloy, ferrite, iron, chromium, cobalt-based
amorphous metal, or the like may be used. As the conductor having
high conductivity, for example, aluminum which has a magnetic field
reduction function due to an eddy current effect may be used. The
main body 302a may be formed by alternately stacking a
ferromagnetic material and a conductor having high conductivity. In
the present embodiment, for example, the main body 302a is formed
by alternately staking an aluminum plate and a permalloy plate as
two layers whose entire thickness is about 20 mm to 30 mm.
[0342] First correction coils (first Helmholtz coils 302c) as a
magnetic shield unit are provided at ends on the +Y direction side
and the -Y direction side of the main body 302a. The first
Helmholtz coils 302c are coils for correcting an entering magnetic
field which enters the internal space of the main body 302a. The
entering magnetic field indicates an external magnetic field which
passes through the first opening 302b and enters the internal
space. The entering magnetic field is strongest with respect to the
first opening 302b in the Y direction. The first Helmholtz coils
302c generate a magnetic field which cancels out the entering
magnetic field by using a current.
[0343] The table 303 is provided with a foundation 307. The
foundation 307 is disposed on the bottom inside the main body 302a,
and extends from the inside of the main body 302a to the outside of
the first opening 302b through the first opening 302b in the Y
direction (in which the subject 306 is movable). A pair of
Y-direction rails 308 extending in the Y direction is provided on
the foundation 307. A Y-direction table 309 which is moved in the Y
direction as a second direction 309a along the Y-direction rails
308 is provided on the Y-direction rails 308. A Y-direction linear
motion mechanism 310 which moves the Y-direction table 309 is
provided between the two Y-direction rails 308.
[0344] A Z-direction table 311 is provided on the Y-direction table
309, and a lifting device (not illustrated) is provided between the
Y-direction table 309 and the Z-direction table 311. The lifting
device lifts the Z-direction table 311. Six X-direction rails 312
extending in the X direction are provided on a surface on the +Z
direction side of the Z-direction table 311. An X-direction table
313 which is moved in the X direction along the X-direction rails
312 is provided on the X-direction rails 312.
[0345] An X-direction linear movement mechanism 314 which moves the
X-direction table 313 in the X direction as a third direction 313d
is provided on the -Y direction side on the Z-direction table 311.
The X-direction linear movement mechanism 314 includes a pair of
bearing portions 314a, and the bearing portions 314a are provided
to be erect on the Z-direction table 311. The X-direction table 313
is located between the two bearing portions 314a. The two bearing
portions 314a rotatably support a first screw rod 314b. A first
penetration hole (not illustrated) which penetrates in the X
direction is provided in the X-direction table 313, and the first
screw rod 314b is provided to penetrate through the first
penetration hole of the X-direction table 313. A female screw (not
illustrated) is formed on the first penetration hole, and the first
screw rod 314b is engaged with the female screw.
[0346] An attachment/detachment portion 315 is provided at one end
on the -X direction side of the first screw rod 314b, and the
attachment/detachment portion 315 is fixed to the first screw rod
314b. If the attachment/detachment portion 315 is rotated, the
first screw rod 314b is rotated. Since the first screw rod 314b is
engaged with the female screw of the X-direction table 313, if the
first screw rod 314b is rotated, the X-direction table 313 is moved
in the X direction. The attachment/detachment portion 315 is
coupled to a rotation shaft of an X-direction table motor 316 as a
driving source. The X-direction table motor 316 rotates the
attachment/detachment portion 315 so as to move the X-direction
table 313 in the X direction. The X-direction table motor 316 is
coupled to a motor movement portion 317 which moves the X-direction
table motor 316 in the X direction. The X-direction linear movement
mechanism 314 is constituted of the bearing portions 314a, the
first screw rod 314b, the attachment/detachment portion 315, the
X-direction table motor 316, the motor movement portion 317, and
the like. The foundation 307, the Y-direction rails 308, the
Y-direction table 309, the Y-direction linear motion mechanism 310,
the Z-direction table 311, the X-direction rails 312, and the
X-direction table 313 constituting the table 303 are made of
non-magnetic materials such as a wood, a resin, a ceramic, and
non-magnetic metal.
[0347] In the electromagnetic shield device 302, the position
measurement device 305 is provided on the +Z direction side of the
first opening 302b. The position measurement device 305 is a device
used to position the subject 306 or measure a surface shape. The
subject 306 mounted on the table 303 passes through the first
opening 302b. The subject 306 passes near the position measurement
device 305, and thus the position measurement device 305 can easily
irradiate the subject 306 with light beams.
[0348] The magnetic sensor 304 is provided inside the
electromagnetic shield device 302. The magnetic sensor 304 is a
sensor which detects a magnetic field generated from the heart of
the subject 306. The magnetic sensor 304 is fixed to the
electromagnetic shield device 302. The location where the living
body magnetic field measurement apparatus 301 is disposed is
adjusted to a state in which no magnetic field is substantially
present by the electromagnetic shield device 302. Therefore, the
magnetic sensor 304 can measure a magnetic field generated from the
heart without being influenced by noise. The magnetic sensor 304
detects an intensity component of a magnetic field in a first
direction 304a which is the same direction as the Z direction.
[0349] The first direction 304a and the second direction 309a are
directions orthogonal to each other. The first direction 304a and
the third direction 313d are directions orthogonal to each other.
The second direction 309a and the third direction 313d are also
directions orthogonal to each other. The table 303 moves the
subject 306 in the second direction 309a and the third direction
313d orthogonal to each other. The table 303 is moved in an
orthogonal coordinate system, and can thus easily control a
position of the table 303. A direction in which the electromagnetic
shield device 302 extends is the second direction 309a.
[0350] A controller 318 is provided at a location separated from
the first opening 302b. The controller 318 outputs an electric
signal so as to control the living body magnetic field measurement
apparatus 301. Specifically, the controller 318 controls the
electromagnetic shield device 302, the table 303, the magnetic
sensor 304, and the position measurement device 305. A magnetic
field or a residual magnetic field is generated due to the electric
signal of the controller 318, and becomes noise when detected by
the magnetic sensor 304. Since the controller 318 is present at the
location separated from the first opening 302b, the magnetic field
or the residual magnetic field generated from the controller 318
hardly reaches the magnetic sensor 304. As a result, the magnetic
sensor 304 can perform measurement with less noise.
[0351] The controller 318 is provided with a display device 321 and
an input device 322. The display device 321 is a liquid crystal
display (LCD) or an organic light emitting diode (OLED). A
measurement situation, a measurement result, and the like are
displayed on the display device 321. The input device 322 is
constituted of a keyboard, a rotary knob, or the like. An operator
operates the input device 322 so as to input various instructions
such as a measurement starting instruction or a measurement
condition to the living body magnetic field measurement apparatus
301.
[0352] FIG. 24A is a schematic sectional view for explaining a
structure of the shape measurement device, and is a view taken
along the side surface of the electromagnetic shield device 302.
FIG. 24B is a schematic sectional view for explaining a structure
of the shape measurement device, and is a view in which the living
body magnetic field measurement apparatus 301 is viewed from the -Y
direction side. In FIGS. 24A and 24B, the position measurement
device 305 includes a laser scanning unit 305a and an imaging
device 305b. The laser scanning unit 305a is provided on a ceiling
of the main body 302a in the first opening 302b, and emits laser
light 305c as light and a light beam in the -Z direction. A front
face 306a of the subject 306 is irradiated with the laser light
305c. The laser light 305c is reflected from the front face 306a.
The laser scanning unit 305a has a function of performing scanning
with the laser light 305c in the X direction, and a function of
irradiating a single point without scanning. When the laser
scanning unit 305a performs scanning with the laser light 305c, a
reflection point 305d at which the laser light 305c is reflected
from the front face 306a is linear when viewed from the imaging
device 305b. When the laser scanning unit 305a does not perform
scanning with the laser light 305c, the reflection point 305d at
which the laser light 305c is reflected from the front face 306a is
a single point.
[0353] When the subject 306 is positioned, the subject 306 is
mounted on the table 303 so as to be directed upward. The laser
scanning unit 305a irradiates the chest of the subject 306 without
scanning with the laser light 305c. The operator drives the
Y-direction linear motion mechanism 310 so as to move the
Y-direction table 309 in the Y direction. The operator drives the
X-direction linear movement mechanism 314 and the X-direction table
motor 316 so as to move the X-direction table 313 in the X
direction. Positions of the table 303 in the X direction and the Y
direction are adjusted so that the laser light 305c is applied to
the xiphisternum 306e of the subject 306.
[0354] The position measurement device 305 has a function of
applying the laser light 305c as guide light, and a function of
measuring a position. The function of applying guide light is a
function of applying a light beam for guiding a position where the
subject 306 is mounted. The function of measuring a position is a
function of measuring a shape of the subject by irradiating the
subject 306 with a light beam. The position measurement device 305
has the function of applying guide light, and thus the position
measurement device 305 applies a light beam for guiding a position
where the subject 306 is mounted. Therefore, it is possible to
reduce the number of constituent elements compared with a case
where the living body magnetic field measurement apparatus 301
separately includes a constituent element applying guide light and
a constituent element measuring a position.
[0355] The imaging device 305b is provided in the main body 302a
via a support portion 305e. The imaging device 305b is obliquely
provided with respect to an advancing direction of the laser light
305c. The imaging device 305b images reflected light 305f which is
reflected from the front face 306a of the subject 306. In this
case, the laser scanning unit 305a, the reflection point 305d, and
the imaging device 305b form a triangle. The distance between the
laser scanning unit 305a and the imaging device 305b is a known
value. An angle formed between the laser light 305c and the
reflected light 305f can be detected on the basis of an image
captured by the imaging device 305b. Therefore, the position
measurement device 305 can measure the distance between the laser
scanning unit 305a and the reflection point 305d by using a
triangulation method.
[0356] A plane which is separated from the surface on the -Z
direction side of the magnetic sensor 304 by a predetermined
distance in the -Z direction is referred to as a reference plane
323. The reference plane 323 is a plane of a location where a
surface for measuring a magnetic field of the subject 306 is
disposed. The distance between the surface on the -Z direction side
of the magnetic sensor 304 and the reference plane 323 is
preferably equal to or more than 2 mm and equal to or less than 10
mm, and is more preferably 5 mm. At this distance, the subject 306
can be made to come close to the magnetic sensor 304 without
contact therebetween. In the present embodiment, the distance
between the surface on the -Z direction side of the magnetic sensor
304 and the reference plane 323 is, for example, 5 mm. The
reference plane 323 is a plane coming into contact with a surface
of the chest 306c which is swollen when the subject 306 breathes
air. The distance between the laser scanning unit 305a and the
reference plane 323 is a known value. The controller 318 calculates
a distance 324 between the reference plane 323 and the front face
306a of the subject 306.
[0357] FIG. 25A is a perspective view of a three-dimensional image
measured by the position measurement device. As illustrated in FIG.
25A, a three-dimensional image 325 measured by the position
measurement device 305 is a stereoscopic image of the chest of the
subject 306. The position measurement device 305 measures a shape
of the front face 306a of the subject 306 while moving the
Y-direction table 309 in the Y direction. The position measurement
device 305 measures a stereoscopic image of the chest of the
subject 306. The unevenness of the chest is observed on the
three-dimensional image 325. FIG. 25B is a schematic side view of a
stereoscopic image for explaining measurement in the position
measurement device. As illustrated in FIG. 25B, the
three-dimensional image 325 includes a location close to the
reference plane 323 and a location distant from the reference plane
323. In the three-dimensional image 325, a range measured by the
magnetic sensor 304 is set to a magnetic field measurement range
326. FIG. 25B illustrates the magnetic field measurement range 326
in the X direction. The magnetic field measurement range 326 is
also set in the Y direction in the same manner. The controller 318
calculates the shortest distance 324a which is a distance 324 to
the location closest to the reference plane 323 in the magnetic
field measurement range 326 of the three-dimensional image 325.
[0358] FIGS. 26A and 26B are schematic side sectional views
illustrating a structure of the table. FIG. 26A illustrates a state
in which the table 303 is being moved in the -Y direction, and FIG.
26B illustrates a state in which the table 303 is moved into the
living body magnetic field measurement apparatus 301, and a heart
magnetic field of the subject 306 is being measured. As illustrated
in FIG. 26A, the pair of first Helmholtz coils 302c is disposed on
the foundation 307. A shape of the first Helmholtz coil 302c is a
frame shape, and is disposed to surround the main body 302a.
[0359] The Y-direction linear motion mechanism 310 includes a motor
310a as a driving source. A first pulley 310b is provided on a
rotation shaft of the motor 310a, and a second pulley 310c is
rotatably provided at an end on the Y direction side of the
Y-direction linear motion mechanism 310. A timing belt 310d is hung
on the first pulley 310b and the second pulley 310c. A connection
portion 310e is provided on the timing belt 310d, and the
connection portion 310e connects the timing belt 310d to the
Y-direction table 309. When the motor 310a rotates the first pulley
310b, the connection portion 310e is moved in the Y direction by
the torque of the motor 310a. The Y-direction table 309 is moved
due to the movement of the connection portion 310e. Therefore, the
motor 310a can move the Y-direction table 309 in the Y direction.
The motor 310a changes a rotation direction of the first pulley
310b so as to move the Y-direction table 309 in both directions
such as +Y direction and the -Y direction.
[0360] Materials of the Y-direction rails 308, the second pulley
310c, the timing belt 310d, and the connection portion 310e are
non-magnetic materials. The timing belt 310d is made of rubber and
resin. The Y-direction rails 308, the second pulley 310c, and the
connection portion 310e are made of ceramics. Therefore, a portion
of the Y-direction linear motion mechanism 310 entering the
electromagnetic shield device 302 is non-magnetic.
[0361] Four lifting devices 327 are provided side by side in the Y
direction in the Y-direction table 309. Each of the lifting devices
327 has a structure in which three air cylinders are arranged in
the X direction. The lifting device 327 expands and contracts the
air cylinders so as to lift the Z-direction table 311 in the first
direction 304a. Each air cylinder is provided with a length
measurement device (not illustrated), and thus the lifting device
327 can detect a movement amount of the Z-direction table 311. The
respective air cylinders move the Z-direction table 311 by the same
distance, and thus the lifting devices 327 can move the Z-direction
table 311 in parallel. Pneumatic equipment such as a compressor and
an electromagnetic valve (not illustrated) is provided in the
controller 318. The lifting devices 327 are controlled by the
controller 318. The Y-direction table 309, the lifting devices 327,
and the Z-direction table 311 are made of aluminum. Therefore, the
Y-direction table 309, the lifting devices 327, and the Z-direction
table 311 are non-magnetic.
[0362] The X-direction table 313 is provided with wheels 328 which
are in contact with the X-direction rails 312. The wheels 328 are
rotated, and thus the X-direction table 313 can be easily moved in
the X direction. The X-direction table 313, the X-direction rails
312, and the wheels 328 are made of ceramics which are non-magnetic
materials. Therefore, the X-direction table 313, the X-direction
rails 312, and the wheels 328 are non-magnetic. A portion of the
table 303 entering the electromagnetic shield device 302 is
non-magnetic. Consequently, it is possible to prevent magnetization
of the table 303 from influencing measurement of a magnetic
field.
[0363] The magnetic sensor 304 is provided on the ceiling of the
main body 302a via a support member 329. A position of the center
of the magnetic sensor 304 in the Z direction is the central
position between the ceiling of the main body 302a and the bottom
of the main body 302a. A position of the center of the magnetic
sensor 304 in the X direction is the central position between a
wall on the +X direction side of the main body 302a and a wall on
the -X direction side thereof. The distance between the center of
the magnetic sensor 304 in the Y direction and an end on the -Y
direction side of the main body 302a is twice longer than the
distance between the center of the magnetic sensor 304 and the wall
on the +Y direction side of the main body 302a. When the center of
the magnetic sensor 304 is located at this location, it is possible
for the magnetic sensor 304 to be hardly influenced by a magnetic
field which enters the electromagnetic shield device 302 from the
outside thereof.
[0364] Second correction coils (second Helmholtz coils 320) having
a cube frame shape are provided inside the electromagnetic shield
device 302. Specifically, at least three pairs of second correction
coils are provided so as to be orthogonal to each other in the X
direction, the Y direction, and the Z direction. In the second
Helmholtz coil 320 orthogonal to the X direction, a measurement
space in which the subject 306 is disposed during measurement and
the magnetic sensor 304 are interposed between a pair of coils from
the X direction (left/right direction). The second Helmholtz coil
320 orthogonal to the X direction may generate a magnetic field in
the X direction and may cancel out an external magnetic field in
the X direction so that an X component of a magnetic field of the
measurement space and the space in which the magnetic sensor 304 is
disposed is reduced to the extent or less of not having an adverse
effect on measurement. In the second Helmholtz coil 320 orthogonal
to the Y direction, the measurement space and the magnetic sensor
304 are interposed between two pairs of coils (that is, four coils)
from the Y direction (front/rear direction). The second Helmholtz
coil 320 orthogonal to the Y direction may generate a magnetic
field in the Y direction and may cancel out an external magnetic
field in the Y direction so that a Y component of a magnetic field
of the measurement space and the space in which the magnetic sensor
304 is disposed is reduced to the extent or less of not having an
adverse effect on measurement. Since the main body 302a has a
tubular shape extending in the front/rear direction, and an
entering magnetic field is considerable in the Y direction, two
pairs of second Helmholtz coils 320 are provided regarding the Y
direction. In the second Helmholtz coil 320 orthogonal to the Z
direction, the measurement space and the magnetic sensor 304 are
interposed between a pair of coils from the Z direction
(upper/lower direction). The second Helmholtz coil 320 orthogonal
to the Z direction may generate a magnetic field in the Z direction
and may cancel out an external magnetic field in the Z direction so
that a Z component of a magnetic field of the measurement space and
the space in which the magnetic sensor 304 is disposed is reduced
to the extent or less of not having an adverse effect on
measurement. The second Helmholtz coil 320 has a square frame shape
when viewed from each orthogonal direction side, and is disposed so
that the central position of the square frame overlaps the central
position of the magnetic sensor 304. A length of the side of the
square is not particularly limited, but, in the present embodiment,
a length of one side is equal to or more than 75 cm and equal to or
less than 85 cm. In FIGS. 26A and 26B, the shape of the second
Helmholtz coil 320 is a rectangular shape for better viewing, but
is actually a square shape.
[0365] The four second Helmholtz coils 320 having the square frame
shape are disposed at the same interval in the Y direction. When
viewed from the X direction, an outer circumference of the second
Helmholtz coil 320 has a square frame shape, and there is a
structure in which two coils are disposed inside the square frame
shape. The second Helmholtz coil 320 is disposed so that the
central position of the square frame shape overlaps the central
position of the magnetic sensor 304.
[0366] A shape of the second Helmholtz coil 320 viewed from the Z
direction is the same as the shape viewed from the X direction. The
second Helmholtz coil 320 is disposed so that the central position
of the square frame shape overlaps the central position of the
magnetic sensor 304. The second Helmholtz coil 320 has such a
shape, and thus it is possible to further reduce a disturbance
magnetic field in the magnetic sensor 304. Particularly, it is
possible to reduce the influence of a magnetic flux which comes
from the -Y direction side of the electromagnetic shield device
302.
[0367] When the table 303 is located on the -Y direction side of
the electromagnetic shield device 302, a half or more of the table
303 protrudes out of the electromagnetic shield device 302.
Consequently, the subject 306 is easily mounted on the table 303.
When the subject 306 is mounted on the table 303, a height from the
floor to the nose of the subject 306 is smaller than a height from
the floor to the surface on the -Z direction side of the magnetic
sensor 304. Therefore, when the Y-direction table 309 is moved in
the Y direction, the subject 306 does not interfere with the
magnetic sensor 304.
[0368] As illustrated in FIG. 26B, the Y-direction table 309 is
moved in the +Y direction, and then the Z-direction table 311 is
moved up. A distance by which the Z-direction table 311 is moved up
is the shortest distance 324a calculated by the controller 318. A
location measured by the magnetic sensor 304 on a surface of the
chest 306c of the subject 306 is a measured surface 306d. In this
case, the measured surface 306d is located at a location opposing
the magnetic sensor 304, and comes close to the magnetic sensor
304. The distance between the measured surface 306d and the
magnetic sensor 304 becomes 5 mm. The measured surface 306d is
measured by the magnetic sensor 304.
[0369] FIG. 27A is a schematic side view illustrating a structure
of the attachment/detachment portion, and illustrates a separation
state of the attachment/detachment portion 315. As illustrated in
FIG. 27A, an attachment/detachment portion installation stand 330
is provided on the -X direction side of the foundation 307. The
motor movement portion 317 is provided at an end on the -X
direction side on the attachment/detachment portion installation
stand 330. The motor movement portion 317 is constituted of a motor
317a, a screw rod 317b, guide rails 317c, and the like. The motor
317a is provided on the -X direction side on the
attachment/detachment portion installation stand 330, and the guide
rails 317c are provided on the +X direction side of the motor 317a.
The guide rails 317c are provided as a pair, and extend in the X
direction.
[0370] The X-direction table motor 316 is provided on the guide
rails 317c, and the X-direction table motor 316 is reciprocally
moved along the guide rails 317c. A rotation shaft of the motor
317a is provided with the screw rod 317b extending in the X
direction. A penetration hole 316a extending in the X direction is
provided in the X-direction table motor 316, and a female screw is
formed on the penetration hole 316a. The female screw of the
penetration hole 316a is screwed with the screw rod 317b. When the
motor 317a rotates the screw rod 317b, the X-direction table motor
316 is moved in the X direction along the guide rails 317c. A
rotation shaft of the X-direction table motor 316 is provided with
a grooved cylinder 315a. A grooved rod 315b is provided at an end
on the -X direction side of the first screw rod 314b. When the
X-direction table motor 316 is moved in the X direction, the
grooved rod 315b is inserted into the grooved cylinder 315a.
[0371] FIG. 27B is a side view of the grooved rod, and is a view in
which the grooved rod 315b is viewed from an axial direction. As
illustrated in FIG. 27B, grooves are provided on an outer
circumference of the grooved rod 315b in an axial direction. FIG.
27C is a side view of the grooved cylinder, and is a view in which
the grooved cylinder 315a is viewed from an axial direction. As
illustrated in FIG. 27C, grooves extending in the axial direction
are provided on an inner diameter of the grooved cylinder 315a. An
outer circumference shape of the grooved rod 315b is substantially
the same as an inner circumference shape of the grooved cylinder
315a. When the grooved rod 315b is inserted into the grooved
cylinder 315a, the grooves of the grooved cylinder 315a mesh with
the grooves of the grooved rod 315b. Consequently, the torque
applied to the grooved cylinder 315a is transmitted to the grooved
rod 315b.
[0372] FIG. 27D is a schematic side view illustrating a structure
of the attachment/detachment portion, and illustrates a connection
state of the attachment/detachment portion 315. In FIG. 27D, the
motor movement portion 317 moves the X-direction table motor 316 in
the X direction, and thus the grooved rod 315b is inserted into the
grooved cylinder 315a. When the X-direction table motor 316 rotates
the rotation shaft, the grooved rod 315b is rotated due to rotation
of the grooved cylinder 315a. Therefore, when the X-direction table
motor 316 rotates the rotation shaft, the first screw rod 314b
coupled to the grooved rod 315b is rotated. The X-direction table
motor 316 moves the X-direction table 313 in the X direction.
[0373] FIG. 28A is a top sectional view for explaining a
configuration of a tube, and is a view in which the living body
magnetic field measurement apparatus 301 is cut on an XY plane
crossing a support member 329. FIG. 28B is a side sectional view
for explaining a configuration of the tube, and is a view in which
the living body magnetic field measurement apparatus 301 is cut on
a YZ plane along the wall on the -X direction side of the
electromagnetic shield device 302.
[0374] The living body magnetic field measurement apparatus 301 is
provided with a first tube 331 as a tube and a second tube 332 as a
tube. A wire through which electricity for driving the magnetic
sensor 304 flows is provided in the first tube 331. The second tube
332 includes a tube through which air for driving the lifting
devices 327 flows.
[0375] A second opening 302d and a third opening 302e are provided
on a side surface of the -X direction side of the main body 302a.
The first tube 331 is disposed through the second opening 302d and
allows the inside and the outside of the electromagnetic shield
device 302 to communicate with each other. In the second opening
302d, the first tube 331 extends in a third direction 313d
orthogonal to the first direction 304a. In the second opening 302d,
a direction of a magnetic vector passing through the first tube 331
is orthogonal to the first direction 304a. Therefore, the magnetic
vector entering the electromagnetic shield device 302 through the
first tube 331 hardly influences the magnetic sensor 304.
[0376] Similarly, the second tube 332 is disposed through the third
opening 302e and causes the inside and the outside of the
electromagnetic shield device 302 to communicate with each other.
In the third opening 302e, the second tube 332 extends in the third
direction 313d orthogonal to the first direction 304a. In the third
opening 302e, a direction of a magnetic vector entering the
electromagnetic shield device 302 through the second tube 332 is
orthogonal to the first direction 304a. Therefore, the magnetic
vector passing through the second tube 332 hardly influences the
magnetic sensor 304. As a result, the living body magnetic field
measurement apparatus 301 can perform measurement with less
noise.
[0377] The electromagnetic shield device 302 extends in the second
direction 309a. The second direction 309a is a direction orthogonal
to the first direction 304a. The first tube 331 extends in the
second direction 309a along the main body 302a. Therefore,
arrangement is obtained in which the first tube 331 is easily
provided. The first tube 331 extends in the second direction 309a,
and the second direction 309a is orthogonal to the first direction
304a. Therefore, a magnetic vector passing through the first tube
331 hardly influences the magnetic sensor 304. As a result, the
living body magnetic field measurement apparatus 301 can perform
measurement with less noise.
[0378] The second tube 332 has a structure of tending to be bent,
and the second tube 332 is bent twice at a bent portion 332a on the
-Y direction side. When the Y-direction table 309 is moved in the Y
direction, the bent portion 332a also is moved in the Y direction.
Consequently, the second tube 332 can be moved with high durability
without being twisted.
[0379] FIG. 29A is a schematic side view illustrating a structure
of the magnetic sensor, and FIG. 29B is a schematic plan view
illustrating a structure of the magnetic sensor. As illustrated in
FIGS. 29A and 29B, laser light 334 is supplied from a laser light
source 333 to the magnetic sensor 304. The laser light source 333
is provided in the controller 318, and the laser light 334 is
supplied to the magnetic sensor 304 through an optical fiber 335
provided in the first tube 331. The magnetic sensor 304 is coupled
to the optical fiber 335 via an optical connector 336.
[0380] The laser light source 333 outputs the laser light 334 with
a wavelength corresponding to an absorption line of cesium. A
wavelength of the laser light 334 is not particularly limited, but
is set to a wavelength of 894 nm corresponding to the D1-line, in
the present embodiment. The laser light source 333 is a tunable
laser device, and the laser light 334 output from the laser light
source 333 is continuous light with a predetermined light
amount.
[0381] The laser light 334 supplied via the optical connector 336
travels in the +X direction and is applied to a polarization plate
337. The laser light 334 having passed through the polarization
plate 337 is linearly polarized. The laser light 334 is
sequentially applied to a first half mirror 338, a second half
mirror 341, a third half mirror 342, and a first reflection mirror
343. Some of the laser light 334 is reflected by the first half
mirror 338, the second half mirror 341, and the third half mirror
342 so as to travel in the -Y direction. The other light 334 is
transmitted therethrough so as to travel in the +X direction. The
first reflection mirror 343 reflects the entire incident laser
light 334 in the -Y direction. An optical path of the laser light
334 is divided into four optical paths by the first half mirror
338, the second half mirror 341, the third half mirror 342, and the
first reflection mirror 343. Reflectance of each mirror is set so
that light intensities of the laser light beams 334 on the
respective optical paths are the same as each other.
[0382] Next, the laser light 334 is sequentially applied to a
fourth half mirror 344, a fifth half mirror 345, a sixth half
mirror 346, and a second reflection mirror 347. Some of the laser
light 334 is reflected by the fourth half mirror 344, the fifth
half mirror 345, and the sixth half mirror 346 so as to travel in
the +Z direction. The other light 334 is transmitted therethrough
so as to travel in the -Y direction. The second reflection mirror
347 reflects the entire incident laser light 334 in the +Z
direction. A single optical path of the laser light 334 is divided
into four optical paths by the fourth half mirror 344, the fifth
half mirror 345, the sixth half mirror 346, and the second
reflection mirror 347. Reflectance of each mirror is set so that
light intensities of the laser light beams 334 on the respective
optical paths are the same as each other. Therefore, the optical
path of the laser light 334 is divided into the sixteen optical
paths. In addition, reflectance of each mirror is set so that light
intensities of the laser light beams 334 on the respective optical
paths are the same as each other.
[0383] Gas cells 348 are provided on the respective optical paths
of the laser light 334 on the +Z direction side of the fourth half
mirror 344, the fifth half mirror 345, the sixth half mirror 346,
and the second reflection mirror 347. The number of gas cells 348
is 16 in four rows and four columns. The laser light beams 334
reflected by the fourth half mirror 344, the fifth half mirror 345,
the sixth half mirror 346, and the second reflection mirror 347
pass through the gas cells 348. The gas cell 348 is a box having a
cavity therein, and an alkali metal gas is enclosed in the cavity.
The alkali metal is not particularly limited, and potassium,
rubidium, or cesium may be used. In the present embodiment, for
example, cesium is used as the alkali metal.
[0384] A polarization separator 349 is provided on the +Z direction
side of each gas cell 348. The polarization separator 349 is an
element which separates the incident laser light 334 into two
polarization components of the laser light 334, which are
orthogonal to each other. As the polarization separator 349, for
example, a Wollaston prism or a polarized beam splitter may be
used.
[0385] A first photodetector 350 is provided on the +Z direction
side of the polarization separator 349, and a second photodetector
351 is provided on the -Y direction side of the polarization
separator 349. The laser light 334 having passed through the
polarization separator 349 is applied to the first photodetector
350, and the laser light 334 reflected by the polarization
separator 349 is applied to the second photodetector 351. The first
photodetector 350 and the second photodetector 351 output signals
corresponding to an amount of incident laser light 334 to the
controller 318. If the first photodetector 350 and the second
photodetector 351 generate magnetic fields, this may influence
measurement, and thus it is preferable that the first photodetector
350 and the second photodetector 351 are made of a non-magnetic
material. The magnetic sensor 304 includes heaters 352 which are
provided on both sides in the X direction and both sides in the Y
direction. Each of the heaters 352 preferably has a structure in
which a magnetic field is not generated, and may employ, for
example, a heater of a type of performing heating by causing steam
or hot air to pass through a flow passage. Instead of using a
heater, the gas cell 348 may be inductively heated by using a high
frequency voltage.
[0386] The magnetic sensor 304 is disposed on the +Z direction side
of the subject 306. A magnetic vector 353 generated from the
subject 306 enters the magnetic sensor 304 from the -Z direction
side. The magnetic vector 353 passes through the fourth half mirror
344 to the second reflection mirror 347, and then passes through
the gas cell 348. The magnetic vector 353 passes through the
polarization separator 349, and comes out of the magnetic sensor
304.
[0387] The magnetic sensor 304 is a sensor which is called an
optical pumping type magnetic sensor or an optical pumping atom
magnetic sensor. Cesium in the gas cell 348 is heated and is
brought into a gaseous state. The cesium gas is irradiated with the
linearly polarized laser light 334, and thus cesium atoms are
excited so that orientations of magnetic moments can be aligned.
When the magnetic vector 353 passes through the gas cell 348 in
this state, the magnetic moments of the cesium atoms precess due to
a magnetic field of the magnetic vector 353. This precession is
referred to as Larmore precession. The magnitude of the Larmore
precession has a positive correlation with the strength of the
magnetic vector 353. In the Larmore precession, a polarization
plane of the laser light 334 is rotated. The magnitude of the
Larmore precession has a positive correlation with a change amount
of a rotation angle of the polarization plane of the laser light
334. Therefore, the strength of the magnetic vector 353 has a
positive correlation with the change amount of a rotation angel of
the polarization plane of the laser light 334. The magnetic sensor
304 has high sensitivity for a component of the magnetic vector 353
in the first direction 304a, and has low sensitivity for a
component thereof orthogonal to the first direction 304a.
[0388] The polarization separator 349 separates the laser light 334
into two components of linearly polarized light which are
orthogonal to each other. The first photodetector 350 and the
second photodetector 351 respectively detect the strengths of the
two components of linearly polarized light orthogonal to each
other. Consequently, the first photodetector 350 and the second
photodetector 351 can detect a rotation angle of a polarization
plane of the laser light 334. The magnetic sensor 304 can detect
the strength of the magnetic vector 353 on the basis of a change of
the rotation angle of the polarization plane of the laser light
334. An element constituted of the gas cell 348, the polarization
separator 349, the first photodetector 350, and the second
photodetector 351 is referred to as a sensor element 304d. In the
present embodiment, sixteen sensor elements 304d of four rows and
four columns are disposed in the magnetic sensor 304. The number
and arrangement of the sensor elements 304d in the magnetic sensor
304 are not particularly limited. The sensor elements 304d may be
disposed in three or less rows or five or more rows. Similarly, the
sensor elements 304d may be disposed in three or less columns or
five or more columns. The larger the number of sensor elements
304d, the higher the spatial resolution.
[0389] FIG. 30 is an electrical control block diagram of the
controller. As illustrated in FIG. 30, the living body magnetic
field measurement apparatus 301 includes the controller 318
controlling an operation of the living body magnetic field
measurement apparatus 301. The controller 318 includes a central
processing unit (CPU) 354 which performs various calculation
processes as a processor, and a memory 355 which stores various
information. A shape sensor driving device 356, a table driving
device 357, the electromagnetic shield device 302, a magnetic
sensor driving device 358, the display device 321, and the input
device 322 are coupled to the CPU 354 via an input/output interface
361 and a data bus 362.
[0390] The shape sensor driving device 356 is a device which drives
the laser scanning unit 305a and the imaging device 305b. The shape
sensor driving device 356 drives the laser scanning unit 305a to
emit the laser light 305c toward the subject 306. The shape sensor
driving device 356 performs scanning with the laser light 305c in
the horizontal direction. The shape sensor driving device 356
drives the imaging device 305b to capture an image of the
reflection point 305d. In addition, the shape sensor driving device
356 irradiates a single location without scanning with the laser
light 305c. The irradiated reflection point 305d is a guiding mark
indicating a location where the subject 306 is positioned.
[0391] The table driving device 357 is a device which drives the
X-direction table 313, the Y-direction table 309, the Z-direction
table 311, and the motor movement portion 317. The table driving
device 357 receives an instruction signal for moving a position of
the X-direction table 313 from the CPU 354. The X-direction table
313 can be moved only when the Y-direction table 309 is located at
a predetermined position. For this reason, first, the Y-direction
table 309 is moved to the predetermined position. The table driving
device 357 detects a position of the Y-direction table 309. The
Y-direction table 309 includes a length measurement device
detecting a position thereof, and the length measurement device
detects a position of the Y-direction table 309. The table driving
device 357 moves the Y-direction table 309, and thus the
Y-direction table 309 is moved to a location where the grooved rod
315b opposes the grooved cylinder 315a.
[0392] Next, the table driving device 357 drives the motor movement
portion 317 so that the grooved cylinder 315a is combined with the
grooved rod 315b. Successively, the table driving device 357
detects a position of the X-direction table 313. The X-direction
table 313 includes a length measurement device detecting a position
thereof, and the length measurement device detects a position of
the X-direction table 313. A difference between a position to which
the X-direction table 313 is scheduled to be moved and the present
position of the X-direction table 313 is calculated. The table
driving device 357 drives the X-direction table motor 316 to move
the X-direction table 313 to the position to which the X-direction
table 313 is scheduled to be moved. Consequently, the table driving
device 357 can move the X-direction table 313 to the location for
which an instruction is given. Successively, the table driving
device 357 drives the motor movement portion 317 to separate the
grooved cylinder 315a from the grooved rod 315b.
[0393] Similarly, the table driving device 357 receives an
instruction signal for moving a position of the Y-direction table
309 from the CPU 354. The table driving device 357 detects a
position of the Y-direction table 309. A difference between a
position to which the Y-direction table 309 is scheduled to be
moved and the present position of the Y-direction table 309 is
calculated. The table driving device 357 drives the motor 310a to
move the Y-direction table 309 to the position to which the
Y-direction table 309 is scheduled to be moved. Consequently, the
table driving device 357 can move the Y-direction table 309 between
the position inside the electromagnetic shield device 302 and the
position outside the electromagnetic shield device 302. In a case
where the position measurement device 305 measures the chest 306c
of the subject 306, the Y-direction table 309 is moved at a
constant speed.
[0394] Similarly, the table driving device 357 receives an
instruction signal for moving a position of the Z-direction table
311 from the CPU 354. Each of the lifting devices 327 lifting the
Z-direction table 311 includes a length measurement device
detecting a position of the Z-direction table 311, and the table
driving device 357 detects a position of the Z-direction table 311.
A difference between a position to which the Z-direction table 311
is scheduled to be moved and the present position of the
Z-direction table 311 is calculated. The lifting device 327 is an
air cylinder, and the table driving device 357 is provided with
pneumatic equipment such as a compressor or an electromagnetic
valve driving the lifting device 327. The table driving device 357
controls an amount of air supplied to the lifting device 327 so as
to move the Z-direction table 311 to the position to which the
Z-direction table 311 is scheduled to be moved.
[0395] The electromagnetic shield device 302 includes the first
Helmholtz coil 302c and a sensor detecting an internal magnetic
field. The electromagnetic shield device 302 reduces an internal
magnetic field of the main body 302a by driving the first Helmholtz
coil 302c in response to an instruction from the CPU 354.
[0396] The magnetic sensor driving device 358 is a device driving
the magnetic sensor 304 and the laser light source 333. The
magnetic sensor 304 is provided with the first photodetector 350,
the second photodetector 351, and the heater 352. The magnetic
sensor driving device 358 drives the laser light source 333, the
heater 352, the first photodetector 350, and the second
photodetector 351. The magnetic sensor driving device 358 drives
the laser light source 333 to supply the laser light 334 to the
magnetic sensor 304. The magnetic sensor driving device 358 drives
the heater 352 so that the magnetic sensor 304 is maintained at a
predetermined temperature. The magnetic sensor driving device 358
converts electric signals output from the first photodetector 350
and the second photodetector 351 into digital signals which are
then output to the CPU 354.
[0397] The display device 321 displays predetermined information in
response to an instruction from the CPU 354. The operator operates
the input device 322 on the basis of the display content and inputs
the instruction content. The instruction content is transmitted to
the CPU 354.
[0398] The memory 355 is a concept including a semiconductor memory
such as a RAM or a ROM, a hard disk, and an external storage device
such as a DVD-ROM. In terms of a function, a storage region for
storing program software 363 in which control procedures of an
operation of the living body magnetic field measurement apparatus
301 are described, or a storage region for storing measurement
portion shape data 364 which is data obtained by measuring a
stereoscopic shape of the magnetic field measurement range 326 of
the subject 306 is set. In addition, a storage region for storing
table movement amount data 365 which is data regarding movement
amounts of the Y-direction table 309, and the Z-direction table 311
is set.
[0399] Further, a storage region for storing magnetic sensor
related data 366 which is data such as parameters used to drive the
magnetic sensor 304 is set in the memory 355. Furthermore, a
storage region for storing magnetic measurement data 367 which is
data measured by the magnetic sensor 304 is set in the memory 355.
Moreover, a storage region functioning as a work area for the CPU
354, a temporary file, or the like, and other various storage
regions are set.
[0400] The CPU 354 controls measurement of a magnetic field
generated from the heart of the subject 306 according to the
program software 363 stored in the memory 355. As a specific
function realizing unit, the CPU 354 includes a shape measurement
control unit 368 which is a position measurement unit. The shape
measurement control unit 368 controls measurement of a stereoscopic
shape of the magnetic field measurement range 326 of the subject
306 by driving the position measurement device 305 and the
Y-direction table 309. The CPU 354 includes a shortest distance
calculation unit 369. The shortest distance calculation unit 369
calculates the shortest distance 324a by using a measurement result
of the stereoscopic shape of the subject 306.
[0401] The CPU 354 includes a table movement control unit 370. The
table movement control unit 370 controls movement and stoppage
positions of the X-direction table 313, and the Y-direction table
309, the Z-direction table 311. The CPU 354 includes an
electromagnetic shield control unit 371. The electromagnetic shield
control unit 371 performs control for minimizing a magnetic field
around the magnetic sensor 304 by driving the electromagnetic
shield device 302.
[0402] The CPU 354 includes a magnetic sensor control unit 372. The
magnetic sensor control unit 372 performs control for causing the
magnetic sensor driving device 358 to drive the magnetic sensor 304
to detect the strength of the magnetic vector 353. The CPU 354
includes a laser pointer control unit 373. The laser pointer
control unit 373 performs control for driving the laser scanning
unit 305a to apply the laser light 305c to only a single point of a
predetermined location.
[0403] In the present embodiment, the above-described respective
functions of the living body magnetic field measurement apparatus
301 are realized in the program software by using the CPU 354, but,
in a case where the above-described respective functions can be
realized by a stand-alone electronic circuit (hardware) without
using the CPU 354, such an electronic circuit may be used.
[0404] Next, a description will be made of a magnetic field
measurement method using the above-described living body magnetic
field measurement apparatus 301 with reference to FIGS. 31 to 33C.
FIG. 31 is a flowchart illustrating a living body magnetic field
measurement method. In the flowchart illustrated in FIG. 31, step
S21 is a subject mounting step. In this step, the subject 306 is
mounted on the X-direction table 313. Next, the flow proceeds to
step S22. Step S22 is a positioning step. In this step, the laser
scanning unit 305a irradiates one location of the chest 306c with
the laser light 305c. In this step, the operator operates the input
device 322 so that the X-direction table 313 and the Y-direction
table 309 are moved, and thus the xiphisternum 306e of the subject
306 is irradiated with the reflection point 305d. Next, the flow
proceeds to step S23.
[0405] Step S23 corresponds to a measured surface shape measurement
step. In this step, the shape measurement control unit 368 drives
the Y-direction table 309 and the position measurement device 305
to measure a stereoscopic shape of the measured surface 306d of the
subject 306. Next, the flow proceeds to step S24. Step S24 is a
shortest distance calculation step. In this step, the shortest
distance calculation unit 369 calculates the shortest distance 324a
by using data regarding the measured stereoscopic shape. Next, the
flow proceeds to step S25.
[0406] Step S25 is a table movement step. In this step, the table
movement control unit 370 moves the table 303 so that the chest
306c of the subject 306 is moved to a location opposing the
magnetic sensor 304. The measured surface 306d of the subject 306
comes close to the magnetic sensor 304. Next, the flow proceeds to
step S26. Step S26 is a measurement step. In this step, the
magnetic sensor control unit 372 causes the magnetic sensor driving
device 358 to drive the magnetic sensor 304. The magnetic sensor
304 detects a magnetic field coming out of the chest 306c of the
subject 306. Through the above steps, the process of measuring a
magnetic field of the subject 306 is finished.
[0407] Next, with reference to FIGS. 32A to 33C, the living body
magnetic field measurement method will be described in more detail
so as to correspond to the steps illustrated in FIG. 31. FIGS. 32A
to 33C are schematic diagrams for explaining the living body
magnetic field measurement method. FIG. 32A is a diagram
corresponding to the subject mounting step of step S21. As
illustrated in FIG. 32A, in step S21, the subject 306 is mounted on
the X-direction table 313. A half or more of the X-direction table
313 protrudes out of the electromagnetic shield device 302. The
Z-direction table 311 is located at a low position, and thus the
subject 306 easily moves onto the X-direction table 313.
[0408] FIGS. 32A and 32B are diagrams corresponding to the
positioning step of step S22. As illustrated in FIG. 32A, in step
S22, the operator operates the input device 322 so as to input an
instruction for starting positioning. The laser pointer control
unit 373 outputs an instruction signal for applying the laser light
305c, to the shape sensor driving device 356. The shape sensor
driving device 356 receives the instruction signal so as to drive
the laser scanning unit 305a. The laser scanning unit 305a performs
irradiation with the laser light 305c in the -Z direction. The
laser light 305c is applied to a single point located in the -Z
direction from the laser scanning unit 305a.
[0409] As illustrated in FIG. 32B, the xiphisternum 306e is present
on the -Y direction side of the chest 306c in the subject 306. The
xiphisternum 306e is a protrusion which protrudes at the lower end
of sternum, and is present at a part called the pit of the stomach
at which the rib bows join together. Referring to FIG. 32A again,
the operator operates the input device 322 so as to input an
instruction for moving the X-direction table 313 in the X
direction. The table movement control unit 370 outputs a signal for
moving the X-direction table 313, to the table driving device 357.
The table driving device 357 drives the motor movement portion 317
to move the X-direction table motor 316 in the +X direction.
Consequently, the grooved cylinder 315a is connected to the grooved
rod 315b.
[0410] Next, the table driving device 357 rotates the X-direction
table motor 316 to move the X-direction table 313 in the X
direction. The X-direction table 313 is moved in tracking of an
instruction which is input by the operator via the input device
322. The operator causes the Y direction side of the xiphisternum
306e to be irradiated with the laser light 305c.
[0411] Successively, the operator operates the input device 322 so
as to input an instruction for moving the Y-direction table 309.
The table movement control unit 370 outputs a signal for moving the
Y-direction table 309, to the table driving device 357. The table
driving device 357 drives the motor movement portion 317 to move
the X-direction table motor 316 in the -X direction. Consequently,
the grooved cylinder 315a is separated from the grooved rod
315b.
[0412] Next, the table driving device 357 rotates the motor 310a to
move the Y-direction table 309 in the Y direction. The Y-direction
table 309 is moved in tracking of an instruction which is input by
the operator via the input device 322. The operator causes the
xiphisternum 306e to be irradiated with the laser light 305c.
Thereafter, the operator operates the input device 322 so as to
input information indicating that positioning of the subject 306
has been finished.
[0413] A reference point 304b for checking a measurement point is
set in the magnetic sensor 304. A position of the reference point
304b in the X direction is the same as the position in the X
direction where the laser light 305c is applied in step S22. A
distance in the Y direction between the position of the reference
point 304b and a position through which the laser light 305c passes
is set to a predetermined reference distance 304c.
[0414] FIG. 32C is a diagram corresponding to the measured surface
shape measurement step of step S23 and the shortest distance
calculation step of step S24. In step S23, the operator causes the
subject 306 to take a normal breath. The subject 306 may take a
deep breath so as to control his or her breathing. The operator
operates the input device 322 so as to input an instruction for
starting measurement of a stereoscopic shape of the measured
surface 306d. The shape measurement control unit 368 receives the
instruction for starting measurement, and outputs an instruction
signal for applying the laser light 305c, to the shape sensor
driving device 356. As illustrated in FIG. 32C, the laser scanning
unit 305a irradiates the measured surface 306d with the laser light
305c, and reciprocally moves the reflection point 305d in the X
direction. The imaging device 305b receives the reflected light
305f. Since the reflection point 305d is reciprocally moved on the
measured surface 306d, the imaging device 305b captures an image in
which the reflection point 305d forms a line. The shape sensor
driving device 356 calculates a distance from the laser scanning
unit 305a to the reflection point 305d by using the image data and
a triangulation method, and outputs the calculated distance to the
memory 355. The memory 355 stores data regarding the distance from
the laser scanning unit 305a to the reflection point 305d as a part
of the measurement portion shape data 364.
[0415] The shape measurement control unit 368 outputs an
instruction signal for moving the Y-direction table 309 to the
table driving device 357 in cooperation with the table movement
control unit 370. A movement range of the Y-direction table 309 is
the same as the magnetic field measurement range 326. The table
driving device 357 moves the Y-direction table 309 in the -Y
direction and then moves the Y-direction table 309 in the +Y
direction at a predetermined speed. The table driving device 357
outputs data indicating a position of the Y-direction table 309 in
the Y direction to the memory 355. Consequently, the measurement
portion shape data 364 of the memory 355 accumulates data regarding
the distance between the laser scanning unit 305a and the
reflection point 305d in the magnetic field measurement range 326.
When the position measurement device 305 completes the measurement
in the magnetic field measurement range 326, the table movement
control unit 370 outputs an instruction signal for moving the
Y-direction table 309 to the table driving device 357 so that the
xiphisternum 306e is located at the location opposing the laser
scanning unit 305a. The table driving device 357 receives the
instruction signal and moves the Y-direction table 309. The
operator gives a message that the subject 306 may take a deep
breath.
[0416] In step S24, the shortest distance calculation unit 369
calculates the distance 324 between the reference plane 323 and the
measured surface 306d within the magnetic field measurement range
326. The distance 324 is calculated by subtracting a predetermined
value from the distance between the laser scanning unit 305a and
the reflection point 305d measured by the position measurement
device 305. Next, the shortest distance calculation unit 369
calculates the shortest distance 324a which is the shortest
distance among the distances 324 calculated by the shortest
distance calculation unit 369.
[0417] FIG. 33A is a diagram corresponding to the table movement
step of step S25 and the measurement step of step S26. As
illustrated in FIG. 33A, in step S25, the table movement control
unit 370 outputs an instruction signal for moving the Y-direction
table 309, to the table driving device 357. The table driving
device 357 receives the instruction signal so as to move the
Y-direction table 309 by the reference distance 304c in the +Y
direction. Next, the table movement control unit 370 outputs an
instruction signal for moving up the Z-direction table 311, to the
table driving device 357. The table driving device 357 receives the
instruction signal so as to move up the Z-direction table 311 by
the shortest distance 324a in the +Z direction. Consequently, the
location on the measured surface 306d which is closest to the
magnetic sensor 304 matches the reference plane 323.
[0418] As a result, the reference point 304b is located at a
location opposing the xiphisternum 306e, and the measured surface
306d is located at a location opposing the magnetic sensor 304. The
distance between the surface on the -Z direction side of the
magnetic sensor 304 and the measured surface 306d becomes 5 mm.
When the subject 306 takes a normal breath, a state occurs in which
the surface on the -Z direction side of the magnetic sensor 304 is
not in contact with the measured surface 306d. Since the magnetic
sensor 304 vibrates when the measured surface 306d is in contact
with the magnetic sensor 304, the measurement accuracy is reduced.
In the present embodiment, since the measured surface 306d is not
in contact with the magnetic sensor 304, the living body magnetic
field measurement apparatus 301 can detect a magnetic field of the
measured surface 306d with high accuracy.
[0419] If the magnetic sensor 304 becomes distant from the measured
surface 306d, the strength of a magnetic field detected by the
magnetic sensor 304 is in inverse proportion to the square of a
distance from the measured surface 306d. Therefore, detection
performance of the magnetic sensor 304 is reduced as the magnetic
sensor 304 becomes more distant from the measured surface 306d. In
the present embodiment, since the measured surface 306d comes close
to the magnetic sensor 304 to the extent to which the measured
surface 306d is not in contact with the magnetic sensor 304, the
living body magnetic field measurement apparatus 301 can detect a
magnetic field of the measured surface 306d with high accuracy.
[0420] The position measurement device 305 is a device which is
operated by electricity, and a magnetic field is formed in a case
where the position measurement device 305 is operated. Even in a
case where the operation of the position measurement device 305 is
stopped, a residual magnetic field is formed. The magnetic sensor
304 is provided at a location separated from the position
measurement device 305, and is provided inside the electromagnetic
shield device 302. The table 303 is moved from the location where
the position measurement device 305 measures the measured surface
306d to the location where the magnetic sensor 304 measures the
measured surface 306d. Therefore, even if the position measurement
device 305 is separated from the magnetic sensor 304, the measured
surface 306d can be made to come close to the magnetic sensor 304.
As a result, the magnetic sensor 304 can detect a magnetic field of
the measured surface 306d with high accuracy without being
influenced by the position measurement device 305.
[0421] FIGS. 33A to 33C are diagrams corresponding to the
measurement step of step S26. As illustrated in FIG. 33A, in step
S26, the magnetic sensor 304 detects the magnetic vector 353 which
travels in the first direction 304a from the measured surface 306d
of the subject 306. The magnetic sensor control unit 372 outputs an
instruction signal for starting measurement to the magnetic sensor
driving device 358. The magnetic sensor driving device 358 receives
the instruction signal for starting measurement, and drives the
laser light source 333 and the heater 352. The laser light source
333 applies the laser light 334. If light emission of the laser
light source 333 is stabilized, and the magnetic sensor 304 is
stabilized at a predetermined temperature, the measurement is
started. The strength of a magnetic field detected by the magnetic
sensor 304 is output as an electric signal. The magnetic sensor
driving device 358 converts electric signals output from the first
photodetector 350 and the second photodetector 351 into electric
signals indicating the strength of the magnetic field. The magnetic
sensor driving device 358 converts the electric signals indicating
the strength of the magnetic field into digital data which is then
transmitted to the memory 355 as the magnetic measurement data
367.
[0422] In FIG. 33B, a first region 374a to a sixteenth region 374r
indicate regions where the respective sensor elements 304d detect
the magnetic vector 353. The first region 374a to the sixteenth
region 374r are disposed in a lattice form of four rows and four
columns. The xiphisternum 306e is disposed in the second region
374b. In this arrangement, the magnetic sensor 304 can detect the
magnetic vector 353 generated from the heart of the subject 306
without leakage within the range of the first region 374a to the
sixteenth region 374r.
[0423] FIG. 33C illustrates an example of change data of a magnetic
field detected by the magnetic sensor 304. A longitudinal axis
expresses the magnetic field strength, and the strength of an upper
part in FIG. 33C is higher than the strength of a lower part
therein. A transverse axis expresses a change in time, and time
changes from a left part to a right part in FIG. 33C. The strength
of the magnetic vector 353 detected by the sensor element 304d is
referred to as the magnetic field strength. A first change line
375a indicates a change in the magnetic field strength in the
twelfth region 374m, and indicates a change in the magnetic field
strength on the upper left side of the heart. The upper left side
of the heart represents a position in the X direction and the Y
direction. A second change line 375b indicates a change in the
magnetic field strength in the fourth region 374d, and indicates a
change in the magnetic field strength on the lower left side of the
heart. A third change line 375c indicates a change in the magnetic
field strength in the second region 374b, and indicates a change in
the magnetic field strength on the lower right side of the heart. A
fourth change line 375d indicates a change in the magnetic field
strength in the tenth region 374j, and indicates a change in the
magnetic field strength on the upper right side of the heart.
Sixteen magnetic field strength change lines can be obtained from
the magnetic sensor 304. In FIG. 33C, for better viewing, four
change lines are illustrated.
[0424] The first change line 375a has a peak, and then the second
change line 375b has a peak. Next, the third change line 375c has a
peak, and then the fourth change line 375d has a peak. As mentioned
above, the peaks of the magnetic field strength move around the
heart. When the heart does not normally operate, waveforms of the
first change line 375a to the fourth change line 375d are deformed.
Therefore, the operator can diagnose heart diseases of the subject
306 by observing waveforms of the first change line 375a to the
fourth change line 375d.
[0425] After the measurement of a magnetic field is completed, the
Z-direction table 311 is moved down, and the Y-direction table 309
is moved in the -Y direction. The subject 306 leaves the table 303,
and thus the process of measuring a magnetic field from the heart
of the subject 306 is finished.
[0426] As described above, according to the present embodiment, the
following effects are achieved.
[0427] (1) According to the present embodiment, the living body
magnetic field measurement apparatus 301 includes the magnetic
sensor 304, the position measurement device 305, the table 303, and
the controller 318. The magnetic sensor 304 detects a component in
the first direction 304a of the magnetic vector 353 coming out of
the measured surface 306d of the subject 306. The position
measurement device 305 measures a position of the measured surface
306d in the first direction 304a. The subject 306 is mounted on the
table 303, and the table 303 moves the subject 306 in the first
direction 304a. The controller 318 controls a position of the table
303. The controller 318 controls a distance by which the table 303
is moved on the basis of data regarding a relative position between
the magnetic sensor 304 and the measured surface 306d in the first
direction 304a, measured by the position measurement device 305.
The controller 318 performs control so that the distance between
the measured surface 306d and the magnetic sensor 304 is 5 mm.
[0428] If the magnetic sensor 304 becomes distant from the measured
surface 306d, the strength of a magnetic field detected by the
magnetic sensor 304 is in inverse proportion to the square of a
distance from the measured surface 306d. Therefore, detection
performance of the magnetic sensor 304 is reduced as the magnetic
sensor 304 becomes more distant from the measured surface 306d.
Since the magnetic sensor 304 vibrates when the measured surface
306d is in contact with the magnetic sensor 304, the measurement
accuracy is reduced. In the present embodiment, the measured
surface 306d can be made to come close to the magnetic sensor 304
in a range in which the measured surface 306d is not in contact
with the magnetic sensor 304. The position measurement device 305
measures a position of the measured surface 306d relative to the
magnetic sensor 304, and then the table 303 causes the subject 306
to come close to the magnetic sensor 304. Therefore, even if the
position measurement device 305 is separated from the magnetic
sensor 304, the subject 306 can be made to come close to the
magnetic sensor 304. As a result, the magnetic sensor 304 is hardly
influenced by the position measurement device 305, and thus the
living body magnetic field measurement apparatus 301 can detect a
magnetic field of the measured surface 306d with high accuracy.
[0429] (2) According to the present embodiment, the table 303 moves
the subject 306 in the second direction 309a and the third
direction 313d. The second direction 309a and the third direction
313d are orthogonal to the first direction 304a. The second
direction 309a and the third direction 313d intersect each other.
Therefore, the table 303 can move the subject 306 in a direction
along a plane orthogonal to the first direction 304a. As a result,
the table 303 can easily position the subject 306 in the plane
direction orthogonal to the first direction 304a.
[0430] (3) According to the present embodiment, the second
direction 309a is orthogonal to the third direction 313d. The table
303 moves the subject 306 in the second direction 309a and the
third direction 313d orthogonal to each other. Therefore, the table
303 can be moved along the orthogonal coordinate system, and thus
it is possible to easily control a movement position of the table
303.
[0431] (4) According to the present embodiment, the X-direction
table motor 316 moves the table 303 in the third direction 313d.
The X-direction table motor 316 is provided with the
attachment/detachment portion 315 which is located outside the
electromagnetic shield device 302, and allows the X-direction table
313 and the X-direction table motor 316 to be attached to or
detached from each other. The attachment/detachment portion 315
connects the X-direction table 313 to the X-direction table motor
316, and then the X-direction table 313 is moved in the third
direction 313d by using the X-direction table motor 316.
[0432] When the X-direction table 313 is not moved in the third
direction 313d, the attachment/detachment portion 315 detaches the
X-direction table motor 316 from the X-direction table 313. The
X-direction table motor 316 can be located outside the
electromagnetic shield device 302, and the X-direction table 313
can be moved into the electromagnetic shield device 302. Therefore,
it is possible to prevent a magnetic field from the X-direction
table motor 316 from influencing the inside of the electromagnetic
shield device 302. As a result, the magnetic sensor 304 can perform
measurement with less noise.
[0433] (5) According to the present embodiment, the position
measurement device 305 measures a stereoscopic shape of the
measured surface 306d. Therefore, it is possible to detect a
position of a most protruding portion of the measured surface 306d.
As a result, the measured surface 306d can be made to come close to
the magnetic sensor 304 in a range in which the most protruding
portion in the measured surface 306d does not come into contact
with the magnetic sensor 304.
[0434] (6) According to the present embodiment, the position
measurement device 305 scans the measured surface 306d with the
laser light 305c. A location irradiated with the laser light 305c
is measured by using a triangulation method. Therefore, the
position measurement device 305 can detect a position of a most
protruding portion within a range in which scanning is performed
with the laser light 305c.
[0435] (7) According to the present embodiment, the position
measurement device 305 applies the laser light 305c for guiding
positioning of the subject 306. This function is a guide light
irradiation function. The position measurement device 305 measures
a stereoscopic shape of the measured surface 306d. This function is
a position measurement function. The position measurement device
305 has the two functions. Therefore, it is possible to reduce the
number of constituent elements compared with a case where the
living body magnetic field measurement apparatus 301 separately
includes a device having the guide light irradiation function and a
device having the position measurement function. As a result, it is
possible to manufacture the living body magnetic field measurement
apparatus 301 with high productivity.
[0436] (8) According to the present embodiment, the position
measurement device 305 is provided in the first opening 302b. The
subject 306 mounted on the table 303 passes through the first
opening 302b. Therefore, the subject 306 passes near the position
measurement device 305, and thus the position measurement device
305 can easily irradiate the subject 306 with the laser light
305c.
[0437] (9) According to the present embodiment, a portion of the
table 303 which is moved into the electromagnetic shield device 302
is non-magnetic. Therefore, it is possible to prevent magnetization
of the table 303 from influencing measurement of a magnetic
field.
[0438] (10) According to the present embodiment, the
electromagnetic shield device 302 attenuates an entering magnetic
field line. The magnetic sensor 304 and the table 303 are provided
in the electromagnetic shield device 302. The electromagnetic
shield device 302 is provided with the first opening 302b, and the
subject 306 can come in and out of the electromagnetic shield
device 302 via the first opening 302b. The controller 318 is
located at a location separated from the first opening 302b.
[0439] The controller 318 makes an electric signal flow so as to
control the table 303. A magnetic field is generated due to the
electric signal, and becomes noise when detected by the magnetic
sensor 304. In the present embodiment, since the controller 318 is
present at the location separated from the first opening 302b, the
magnetic field generated from the controller 318 hardly reaches the
magnetic sensor 304. As a result, the magnetic sensor 304 can
perform measurement with less noise.
[0440] (11) According to the present embodiment, the
electromagnetic shield device 302 is provided with the first tube
331 and the second tube 332, and the first tube 331 and the second
tube 332 extend in a direction orthogonal to the first direction
304a and allow the inside and the outside of the electromagnetic
shield device 302 to communicate with each other. Directions of
magnetic vectors passing through the first tube 331 and the second
tube 332 are orthogonal to the first direction 304a. Therefore,
magnetic vectors passing through the first tube 331 and the second
tube 332 hardly influence the magnetic sensor 304. As a result, the
magnetic sensor 304 can perform measurement with less noise.
[0441] (12) According to the present embodiment, the first tube 331
and the second tube 332 extend in the second direction 309a, and
the second direction 309a is orthogonal to the first direction
304a. Therefore, magnetic vectors passing through the first tube
331 and the second tube 332 hardly influence the magnetic sensor
304. As a result, the magnetic sensor 304 can perform measurement
with less noise. The first tube 331 and the second tube 332 are
provided along the electromagnetic shield device 302, and
arrangement is obtained in which the first tube 331 the second tube
332 are easily provided.
[0442] (13) According to the present embodiment, in the subject
mounting step of step S21, the subject 306 is mounted on the table
303. In the measured surface shape measurement step of step S23, a
stereoscopic shape of the measured surface 306d of the subject 306
is measured. In the shortest distance calculation step of step S24,
the shortest distance 324a to a most protruding portion of the
stereoscopic shape is calculated. In the table movement step of
step S25, the table 303 is moved so that the most protruding
portion comes close to the magnetic sensor 304 with a predetermined
gap. In the measurement step of step S26, a distribution of the
magnetic vector 353 in the subject 306 is detected.
[0443] Therefore, the magnetic sensor 304 comes close to the
measured surface 306d in a range in which there is no contact
therebetween, and performs measurement. The position measurement
device 305 measures a position of the measured surface 306d
relative to the magnetic sensor 304, and then the table 303 causes
the subject 306 to come close to the magnetic sensor 304.
Therefore, even if the position measurement device 305 is separated
from the magnetic sensor 304, the subject 306 can be made to come
close to the magnetic sensor 304. As a result, the magnetic sensor
304 is hardly influenced by the position measurement device 305,
and thus the living body magnetic field measurement apparatus 301
can detect a magnetic field of the measured surface 306d with high
accuracy.
[0444] (14) According to the present embodiment, the motor 310a of
the Y-direction linear motion mechanism 310 is located outside the
electromagnetic shield device 302. The motor 310a tends to generate
an electromagnetic wave so as to generate a residual magnetic
field. Since the motor 310a of the Y-direction linear motion
mechanism 310 is located outside the electromagnetic shield device
302, the residual magnetic field of the motor 310a hardly
influences the magnetic sensor 304. Therefore, the living body
magnetic field measurement apparatus 301 can detect a magnetic
field of the measured surface 306d with high accuracy.
[0445] The present embodiment is not limited to the above-described
embodiments, and various modifications or alterations may be
employed by a person skilled in the art within the technical spirit
of the invention. Modification examples will be described
below.
Modification Example 1
[0446] In the first embodiment, the shape measurement device 5
irradiates the subject 6 with the laser light 5c, and the imaging
device 5b images the reflection point 5d. A stereoscopic shape of
the measured surface 6d is measured by using an image captured by
the imaging device 5b. Other methods may be used to measure a
surface shape of the measured surface 6d. For example, measurement
may be performed by using an ultrasonic wavelength measurement
device or by using interference of laser light. A stereoscopic
shape may be measured by lifting a contact type displacement gauge
and tracing a surface of the subject 6. An easy measurement method
may be selected.
Modification Example 2
[0447] In the first embodiment, an air cylinder is used in the
lifting device 24. A hydraulic cylinder may be used in the lifting
device 24. Oil is less expandable than air, and thus a movement
amount can be controlled with high accuracy. A manual jack may be
used in the lifting device 24. The device can be simplified.
Modification Example 3
[0448] In the first embodiment, a length measurement device is
provided in the lifting device 24, and a movement amount is
feedback. A lifting distance may be controlled by controlling an
amount of air supplied to the air cylinder. The number of
components can be reduced, and thus it is possible to manufacture
the magnetic field measurement apparatus 1 with high
productivity.
Modification Example 4
[0449] In the first embodiment, the X-direction linear movement
mechanism 14 is of an electric type of being moved by the
X-direction table motor 16. The X-direction linear movement
mechanism 14 may be of a manual type. It is possible to reduce
generation of a magnetic field. The Y-direction linear motion
mechanism 10 of the Y-direction table 9 is of an electric type. The
Y-direction linear motion mechanism 10 may be of a manual type. It
is possible to minimize generation of an electromagnetic wave and
thus to prevent the influence of a residual magnetic field.
Modification Example 5
[0450] In the first embodiment, a magnetic field is measured inside
the electromagnetic shield device 2. When the magnetic field
measurement apparatus 1 is provided in a room in which an
electromagnetic wave is blocked, the electromagnetic shield device
2 may be omitted. The number of components can be reduced, and thus
it is possible to manufacture the magnetic field measurement
apparatus 1 with high productivity.
Modification Example 6
[0451] In the first embodiment, a stereoscopic shape of the
measured surface 6d is measured in a state in which the subject 6
takes a normal breath. A stereoscopic shape of the measured surface
6d may be measured in a state in which the lung is swollen. A most
protruding portion may be detected, and a position of the most
protruding portion may be measured in a state in which the lung is
swollen. Even if the subject 6 swells the lung thereof, it is
possible to prevent the subject 6 from coming into contact with the
magnetic sensor 4.
Modification Example 7
[0452] In the first embodiment, the door 2d is provided at the
opening 2b of the electromagnetic shield device 2. In a case where
an amount of magnetic fields entering the electromagnetic shield
device 2 through the opening 2b is small, the door 2d may be
omitted. The number of components can be reduced, and thus it is
possible to manufacture the magnetic field measurement apparatus 1
with high productivity.
[0453] In a case where the door on the -Y direction side of the
electromagnetic shield device 2 is omitted, positions of the
magnetic sensor 4 and the second Helmholtz coil 28 are preferably
changed. A position of the center of the magnetic sensor 4 in the Y
direction is located further in the +Y direction than an
intermediate position between the wall on the +Y direction side and
the door on the -Y direction side of the main body 2a. A position
of the center of the second Helmholtz coil 28 is set to be the same
as a position of the center of the magnetic sensor 4. If the center
of the magnetic sensor 4 is located at this position, it is
possible for the magnetic sensor 4 to be hardly influenced by a
magnetic field which enters the electromagnetic shield device 2
from the outside thereof.
Modification Example 8
[0454] In the first embodiment, the electromagnetic shield device 2
includes the rectangular tubular main body 2a. Therefore, the
electromagnetic shield device 2 has a quadrangle frame shape as a
sectional shape along a plane orthogonal to the Y direction. The
electromagnetic shield device 2 may have a frame shape such as a
circular shape, a hexagonal shape, or an octagonal shape as a
sectional shape along a plane orthogonal to the Y direction. It is
possible to further reduce a magnetic field in the magnetic sensor
4.
Modification Example 9
[0455] In the first embodiment, in the table movement step of step
S5, the tilting table 18 is tilted with the X direction as an axis.
Next, the tilting table 18 is tilted with the Y direction as an
axis. These operations may be performed in a reverse procedure.
That is, the tilting table 18 may be tilted with the Y direction as
an axis, and then the tilting table 18 may be tilted with the X
direction as an axis. The operations may be performed in an easily
checked procedure. The first tilting portion 26a to the third
tilting portion 26c may be simultaneously expanded so that the
tilting table 18 is tilted. It is possible to reduce tilting
time.
Modification Example 10
[0456] In the first embodiment, in the table movement step of step
S5, the tilting table 18 is tilted, and then the Y-direction table
9 is moved. Next, the Z-direction table 11 is moved up. These
operations may be performed in a reverse procedure. That is, the
Y-direction table 9 is moved in the Y direction, and then the
tilting table 18 is tilted. Next, the Z-direction table 11 may be
moved up.
Modification Example 11
[0457] In the first embodiment, the table 3 is provided with the
lifting device 24 and the tilting device 26. The lifting device 24
and the tilting device 26 may be integrated into a single device.
This device may perform lifting and tilting of the tilting table
18. The number of constituent elements can be reduced, and thus it
is possible to manufacture the magnetic field measurement apparatus
1 with high productivity.
Modification Example 12
[0458] In the first embodiment, the tilting table 18 is supported
by three legs such as the first tilting portion 26a, the second
tilting portion 26b, and the third tilting portion 26c. The tilting
table 18 may be supported by four or more legs. A load applied to
each leg can be reduced.
Modification Example 13
[0459] In the first embodiment, the magnetic sensor 4 detects the
magnetic vector 50 which travels in the first direction 4a. The
magnetic sensor 4 may detect the magnetic vectors 50 with
components in the second direction 9a and the third direction 13d
in addition to the first direction 4a. It is possible to more
finely detect a motion of the heart 6g.
Modification Example 14
[0460] In the first embodiment, the heater 49 heats the magnetic
sensor 4. The heater 49 employs a method in which heating is
performed by making steam or hot air pass through a flow passage.
Heating may be performed by using a heating wire. In this case,
heating is performed before a magnetic field is measured, and
heating using the heating wire is stopped when a magnetic field is
measured. Consequently, the magnetic sensor 4 can be heated without
a magnetic field influencing the magnetic sensor 4. Preferably, a
member with large heat capacity is provided in the magnetic sensor
4 so that the temperature of the magnetic sensor 4 hardly
decreases.
Modification Example 15
[0461] In the second embodiment, the contour measurement section
102 irradiates the subject 109 with the laser light 113c and the
laser light 117c, and the imaging device 113b and the imaging
device 117b capture images of the reflection point 113d and the
reflection point 117d. A surface shape of the subject 109 is
measured by using the images captured by the imaging device 113b
and the imaging device 117b. Other methods may be used to measure a
surface shape of the subject 109. For example, measurement may be
performed by using an ultrasonic wavelength measurement device or
by using interference of laser light. A stereoscopic shape may be
measured by lifting a contact type displacement gauge and tracing a
surface of the subject 109. An easy measurement method may be
selected.
Modification Example 16
[0462] In the second embodiment, an air cylinder is used in the
lifting device 138. A hydraulic cylinder may be used in the lifting
device 138. Similarly, air cylinders are used in the first lifting
portion 142 to the tenth lifting portion 151. Hydraulic cylinder
may be used in the first lifting portion 142 to the tenth lifting
portion 151. Oil is less expandable than air, and thus a movement
amount can be controlled with high accuracy. Manual jacks may be
used in the lifting device 138, and the first lifting portion 142
to the tenth lifting portion 151. The device can be simplified.
Modification Example 17
[0463] In the second embodiment, length measurement devices are
provided in the lifting device 138, and the first lifting portion
142 to the tenth lifting portion 151, and a movement amount is
feedback. A lifting distance may be controlled by controlling an
amount of air supplied to the air cylinder. The number of
components can be reduced, and thus it is possible to manufacture
the living body magnetic field measurement apparatus 101 with high
productivity.
Modification Example 18
[0464] In the second embodiment, the subject 109 is directly
disposed on the contact surface 164. An elastic sheet may be
disposed between the contact surface 164 and the subject 109. It is
possible to distribute a load of the back face 109b of the subject
109. Consequently, it is possible to reduce pain which the subject
109 may feel due to the table 121 being too hard.
Modification Example 19
[0465] In the second embodiment, the X-direction linear movement
mechanism 130 is of a manual type. The X-direction linear movement
mechanism 130 may be of an electric type of being moved by a motor.
It is possible to move the X-direction table 129 with high
operability. The Y-direction linear motion mechanism 126 of the
Y-direction table 125 is of an electric type. The Y-direction
linear motion mechanism 126 may be of a manual type. It is possible
to minimize generation of an electromagnetic wave and thus to
prevent the influence of a residual magnetic field.
Modification Example 20
[0466] In the second embodiment, a magnetic field is measured
inside the electromagnetic shield device 118. When the magnetic
field measurement section 103 is provided in a room in which an
electromagnetic wave is blocked, the electromagnetic shield device
118 may be omitted. The number of components can be reduced, and
thus it is possible to manufacture the living body magnetic field
measurement apparatus 101 with high productivity.
Modification Example 21
[0467] In the second embodiment, widths of the first division
surface 152a to the tenth division surface 163a are the same as
each other. The widths of the first division surface 152a to the
tenth division surface 163a may be different from each other. The
widths which easily match a person's shape may be employed.
Consequently, it is possible to easily bring the contact surface
164 into contact with the back face 109b of the subject 109.
Modification Example 22
[0468] In the second embodiment, the -Y direction side of the
electromagnetic shield device 118 is open without a wall. A door
may be provided at the open location on the -Y direction side of
the electromagnetic shield device 118. A material of the door is
the same as a material of the main body 118a, and is a material
blocking a magnetic field. When the Y-direction table 125 enters
the electromagnetic shield device 118, the door is closed.
Consequently, it is possible to block a magnetic field which
travels toward the magnetic sensor 122 from the -Y direction side
of the electromagnetic shield device 118. As a result, the magnetic
sensor 122 can detect a magnetic field of the subject 109 with
higher accuracy without being influenced by disturbance of the
magnetic field.
[0469] In a case where the door is provided on the -Y direction
side of the electromagnetic shield device 118, positions of the
magnetic sensor 122 and the second Helmholtz coil 139 are
preferably changed. A position of the center of the magnetic sensor
122 in the Y direction is an intermediate position between the wall
on the +Y direction side and the door on the -Y direction side of
the main body 118a. A position of the center of the second
Helmholtz coil 139 is set to be the same as a position of the
center of the magnetic sensor 122. If the center of the magnetic
sensor 122 is located at this position, it is possible for the
magnetic sensor 122 to be hardly influenced by a magnetic field
which enters the electromagnetic shield device 118 from the outside
thereof.
Modification Example 23
[0470] In the fourth embodiment, the position measurement device
305 irradiates the subject 306 with the laser light 305c, and the
imaging device 305b captures an image of the reflection point 305d.
A stereoscopic shape of the measured surface 306d is measured by
using the image captured by the imaging device 305b. Other methods
may be used to measure a stereoscopic surface shape of the measured
surface 306d. For example, measurement may be performed by using an
ultrasonic wavelength measurement device or by using interference
of laser light. A stereoscopic shape may be measured by lifting a
contact type displacement gauge and tracing a surface of the
subject 306. An easy measurement method may be selected.
Modification Example 24
[0471] In the fourth embodiment, an air cylinder is used in the
lifting device 327. A hydraulic cylinder may be used in the lifting
device 327. Oil is less expandable than air, and thus a movement
amount can be controlled with high accuracy. A manual jack may be
used in the lifting device 327. The device can be simplified.
Modification Example 25
[0472] In the fourth embodiment, a length measurement device is
provided in the lifting device 327, and a movement amount is
feedback. A lifting distance may be controlled by controlling an
amount of air supplied to the air cylinder. The number of
components can be reduced, and thus it is possible to manufacture
the living body magnetic field measurement apparatus 301 with high
productivity.
Modification Example 26
[0473] In the fourth embodiment, the X-direction linear movement
mechanism 314 is of an electric type of being moved by the
X-direction table motor 316. The X-direction linear movement
mechanism 314 may be of a manual type. It is possible to reduce
generation of a magnetic field. The Y-direction linear motion
mechanism 310 of the Y-direction table 309 is of an electric type.
The Y-direction linear motion mechanism 310 may be of a manual
type. It is possible to minimize generation of an electromagnetic
wave and thus to prevent the influence of a residual magnetic
field.
Modification Example 27
[0474] In the fourth embodiment, a magnetic field is measured
inside the electromagnetic shield device 302. When the living body
magnetic field measurement apparatus 301 is provided in a room in
which an electromagnetic wave is blocked, the electromagnetic
shield device 302 may be omitted. The number of components can be
reduced, and thus it is possible to manufacture the living body
magnetic field measurement apparatus 301 with high
productivity.
Modification Example 28
[0475] In the fourth embodiment, a stereoscopic shape of the
measured surface 306d is measured in a state in which the subject
306 takes a normal breath. A stereoscopic shape of the measured
surface 306d may be measured in a state in which the lung is
swollen. A most protruding portion may be detected, and a position
of the most protruding portion may be measured in a state in which
the lung is swollen. Even if the subject 306 swells the lung
thereof, it is possible to prevent the subject 306 from coming into
contact with the magnetic sensor 304.
Modification Example 29
[0476] In the fourth embodiment, the -Y direction side of the
electromagnetic shield device 302 is open without a wall. A door
may be provided at the open location on the -Y direction side of
the electromagnetic shield device 302. A material of the door is
the same as a material of the main body 302a, and is a material
blocking a magnetic field. When the Y-direction table 309 enters
the electromagnetic shield device 302, the door is closed.
Consequently, it is possible to block a magnetic field which
travels toward the magnetic sensor 304 from the -Y direction side
of the electromagnetic shield device 302. As a result, the magnetic
sensor 304 can detect a magnetic field of the subject 306 with
higher accuracy without being influenced by disturbance of the
magnetic field.
[0477] In a case where the door is provided on the -Y direction
side of the electromagnetic shield device 302, positions of the
magnetic sensor 304 and the second Helmholtz coil 320 are
preferably changed. A position of the center of the magnetic sensor
304 in the Y direction is an intermediate position between the wall
on the +Y direction side and the door on the -Y direction side of
the main body 302a. A position of the center of the second
Helmholtz coil 320 is set to be the same as a position of the
center of the magnetic sensor 304. If the center of the magnetic
sensor 304 is located at this position, it is possible for the
magnetic sensor 304 to be hardly influenced by a magnetic field
which enters the electromagnetic shield device 302 from the outside
thereof.
Modification Example 30
[0478] In the fourth embodiment, the electromagnetic shield device
302 includes the rectangular tubular main body 302a. Therefore, the
electromagnetic shield device 302 has a quadrangle frame shape as a
sectional shape along a plane orthogonal to the Y direction. The
electromagnetic shield device 302 may have a frame shape such as a
circular shape, a hexagonal shape, or an octagonal shape as a
sectional shape along a plane orthogonal to the Y direction. It is
possible to further reduce a magnetic field in the magnetic sensor
304.
Modification Example 31
[0479] In the fourth embodiment, the imaging device 305b captures
the three-dimensional image 325, and the shortest distance
calculation unit 369 calculates the shortest distance 324a. The
operator may select a location which is closest to the reference
plane 323 in the measured surface 306d, and the location may be
measured alone. In other words, the distance 324 may be measured at
the location which is highest from the table 303 in the measured
surface 306d. The measured value may be used as the shortest
distance 324a. It is possible to efficiently measure the shortest
distance 324a within a short period of time.
[0480] The entire disclosure of Japanese Patent Application No.
2015-116409, filed Jun. 9, 2015 is expressly incorporated by
reference herein.
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